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Gear Talk => EOS Bodies - For Stills => Topic started by: J.R. on January 19, 2013, 11:44:34 AM

Title: ISO 50
Post by: J.R. on January 19, 2013, 11:44:34 AM
I was just going through some EOS reading material and came across this regarding ISO 50 expansion ... "There will be approximately one less stop of DR in the highlights at ISO 50". So if I am reading this correctly ISO 50 is just empty night showing a "correct" exposure without any use ...

Is my understanding correct or am I missing something?
Title: Re: ISO 50
Post by: sanj on January 19, 2013, 11:55:37 AM
No JR.
I find 50 asa to be 'smoother' than 100.
And YES it seems like DR is reduced when shooting at 50, but if on a tripod you could bracket and merge in PS.
I so prefer to use ISO 50 when my camera is on tripod or when I have enough light.

Perhaps you should make a test and judge for yourself. If you do, I would love to know your thoughts. Please send me a personal message as I might miss your reply here.

This is of interest to me.

Best...
Title: Re: ISO 50
Post by: J.R. on January 19, 2013, 12:06:13 PM
Thanks Sanjay (I checked out your website :))

I've used it only when I want to slow things down and it was not possible otherwise. Because it is "expansion", i believe (unless proven otherwise) that there must be a compromise somewhere. I generally use the NDX rather than the ISO 50.

i must say I have noted very little difference except low recovery from the highlights. I think I might as well do a test! ... Will get back to you on PM.

Cheers ... J.R.
Title: Re: ISO 50
Post by: RLPhoto on January 19, 2013, 12:51:10 PM
I used ISO 50 a lot in my 5Dc because of how super smooth the files looked. The 5d3, not so much.
Title: Re: ISO 50
Post by: Jesse on January 19, 2013, 12:52:07 PM
There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.
Title: Re: ISO 50
Post by: J.R. on January 19, 2013, 01:07:54 PM
There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

I used ISO 50 a lot in my 5Dc because of how super smooth the files looked. The 5d3, not so much.

So basically my hunch appears to be right ... It's useless except for reporting the correct exposure
Title: Re: ISO 50
Post by: Sporgon on January 19, 2013, 01:11:48 PM
There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

I'm not sure it's that simple. Why do you get less highlight range ?

If you have to under expose more to hold highlight, is the shadow recovery improved enough to give more benefit from just using ISO 100 and greater exposure ?

I too though files were better on 5Dc at 50, but it may be psychological   :)
Title: Re: ISO 50
Post by: neuroanatomist on January 19, 2013, 01:29:07 PM
There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.
Title: Re: ISO 50
Post by: ilkersen on January 19, 2013, 02:29:54 PM
Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.

Let's say I have a "right exposed" image at ISO 100, and I go down to ISO 50 in AV mode.  Shutter speed doubles.  If the sensor was acting as if at ISO 100, it would saturate at the longer exposure and I would get blown out highlights at 50 (maybe more towards gray than white), but not at 100.  I'm not entirely convinced this is how it works.  I wish I knew where and how the expansion is executed in the camera. 
Title: Re: ISO 50
Post by: TrumpetPower! on January 19, 2013, 03:22:16 PM
There might be a bit of analog jiu-jitsu contributing to the mix, but, with that caveat, the linear data recorded at the sensor with a shot at, say f/8 @ 1/400 @ ISO 100 ("sunny f/16") will be identical to the same shot at f/8 @ 1/400 @ ISO 50. At some point in the processing chain, however, the values in the ISO 50 file will get halved (by simple arithmetic, not electronic amplification), resulting in an image one stop darker than the ISO 100 file. That will reduce noise overall. However, the sensor is still saturating at the exact same point. The net effect is that a pixel that the sensor recorded as, say 256, is being rendered as 128...and that there's nothing in the original data that gets mapped between 128 and 256.

Thanks to the gamma curve that gets applied after linear processing, the end result is that there's no data in the last stop. It therefore gets rendered as pure white -- and, thus, a loss of a stop.

You can do the exact same thing yourself, assuming your RAW processing software is capable of linear exposure adjustments.

It's potentially useful in scenes with low dynamic range, or in scenes where you don't care about highlights but do care about shadows.

The common term amongst photographers who do that sort of thing is, "ETTR." I generally strongly caution against doing that, as it's very easy to blow out the highlights, and there's so much wonderful and delicate color to be found in the highlights that is so easy to clobber. But there are certainly situations in which it can be useful.

In general, the meter in most cameras underexposes the linear data by one to two stops, and the processing pipeline applies an equal and opposite amount of digital overexposure to compensate. This is generally a very good thing, because sensors clip so readily and so unforgivingly and modern sensors have so little noise. But, yes, if you're very careful, you can make use of that "extra" headroom.

Cheers,

b&
Title: Re: ISO 50
Post by: phoenix on January 19, 2013, 03:31:28 PM
you can also use it to sync your flashes at 1 stop lower aperture giving you better subject isolation. especially useful now that cameras are coming out with slower syncs.
Title: Re: ISO 50
Post by: neuroanatomist on January 19, 2013, 03:55:52 PM
Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.

Let's say I have a "right exposed" image at ISO 100, and I go down to ISO 50 in AV mode.  Shutter speed doubles.  If the sensor was acting as if at ISO 100, it would saturate at the longer exposure and I would get blown out highlights at 50 (maybe more towards gray than white), but not at 100.  I'm not entirely convinced this is how it works.  I wish I knew where and how the expansion is executed in the camera.

Expanded ISO means digital gain (negative gain for ISO 50).  The exposure is at ISO 100, then pulled down a stop.  In your example, you'd lose the highlights.
Title: Re: ISO 50
Post by: TrumpetPower! on January 19, 2013, 04:33:39 PM
Expanded ISO means digital gain (negative gain for ISO 50).  The exposure is at ISO 100, then pulled down a stop.  In your example, you'd lose the highlights.

-- assuming, of course, there are highlights to be lost.

There almost always are, which is why ETTR is generally not such a great idea. But, when there aren't, or when you truly don't care about losing them, then, yes, ISO 50 or ETTR is a sometimes-useful tool to have in the toolbox.

b&
Title: Re: ISO 50
Post by: Marsu42 on January 19, 2013, 05:33:45 PM
well there are a benefit with Canon sensors= less noise in the shadows=richer exposed but you lose 1stop DR

Interesting, though for the 6d at least dpreview cannot see any advantage except for skipping a nd filter: http://www.dpreview.com/previews/canon-eos-6d/7 (http://www.dpreview.com/previews/canon-eos-6d/7)

Quote
The EOS 6D's lowest standard ISO is 100 but it can offer ISO 50 as an extended mode. Essentially this is doing the opposite of Highlight Tone priority mode - it's increasing the exposure by a stop, then using a different tone curve to pull the image brightness down to compensate. However, whereas HTP mode attempts to protect the image from highlight clipping, switching to ISO 50 makes it far more likely.

Because it's all-but impossible to recover over-exposed highlights, we'd recommend not using the camera's ISO 50 unless you have a specific reason - in everyday shooting you'd generally be better off using a neutral density filter if you need the longer shutter speeds. That's not to say that it's useless though; if you're shooting under controlled lighting and can be confident of retaining highlights, it should give the best quality.
Title: Re: ISO 50
Post by: Marsu42 on January 19, 2013, 06:19:27 PM
so regarding of the subject (motive with no high lights = motive with a small DR) you can overexpose and get a benefit of the over exposure in the shadows

That's great information, thanks! I'll certainly use that once I've got a 6d and am doing tripod macro focus stacks with low dr objects.
Title: Re: ISO 50
Post by: TrumpetPower! on January 19, 2013, 07:35:35 PM
so regarding of the subject (motive with no high lights = motive with a small DR) you can overexpose and get a benefit of the over exposure in the shadows

That's great information, thanks! I'll certainly use that once I've got a 6d and am doing tripod macro focus stacks with low dr objects.

If you're going to the trouble of focus stacking...well, first, with macro work, there's often all sorts of specular highlights with lots of colorful interference patterns and other things going on, such that you might have a great deal more dynamic range in the scene that you want to preserve than you initially realize.

But, back to point...if you're focus stacking, there's no reason you can't either do "standard" ETTR (if it truly is a scene with a limited dynamic range) or HDR (if necessary). You've already got a workflow that involves lots of scripted steps; what's one more step to script?

I would note, though, that the exposure adjustments for either ETTR or the type of not-tonemapped HDR you'd want are really best done in the camera's native linear space before any sort of gamma or other tone curve is applied. I don't know if ACR / Lightroom does that, but most tools based off DCRAW do. I'd especially recommend Raw Photo Processor: http://www.raw-photo-processor.com/ (http://www.raw-photo-processor.com/)

If your tool of choice doesn't do exposure adjustments in linear raw space, then you're best off nailing exposure in camera, and ISO 50 therefore becomes (in that situation) a better bet than ETTR.

Cheers,

b&
Title: Re: ISO 50
Post by: Marsu42 on January 19, 2013, 08:05:10 PM
Thanks for the further explanation, I have to admit I didn't think this far :-o

Btw I always try to get around using hdr for focus stacking because using more than 100 shutter cycles for one resulting pictures is really something I only like to do if I know the shot will be stellar.

If you're going to the trouble of focus stacking...well, first, with macro work, there's often all sorts of specular highlights
Agreed, but there are also some low contrast scenes esp. in evening hours, I've shot enough stacks to be able to tell by now.

I don't know if ACR / Lightroom does that, but most tools based off DCRAW do. I'd especially recommend Raw Photo Processor

I'm afraid I'm running good ol' Windows so that tool would be only available in a MacOSX vm and I doubt it'd be worth the hassle, esp. since I'd end up having a demosaiced 100mb tif instead of a 20mb raw dng.

But I'm hopeful that in LR's raw processing adjusting the exposure doesn't collide with tone curves either applied manually or via picture styles.

If your tool of choice doesn't do exposure adjustments in linear raw space, then you're best off nailing exposure in camera, and ISO 50 therefore becomes (in that situation) a better bet than ETTR.

At least with the 60d I'm usually doing ettr and highlight recovery in Lightroom to get more shadow resolution. Since I haven't got a 6d with iso50 (yet) I'm unable to do a test the difference, but if I understand you correctly you're saying that if the postprocessing software is capable of operating in raw space iso50 should be equal to ettr @iso100?
Title: Re: ISO 50
Post by: TrumpetPower! on January 19, 2013, 08:24:44 PM
I don't know if ACR / Lightroom does that, but most tools based off DCRAW do. I'd especially recommend Raw Photo Processor

I'm afraid I'm running good ol' Windows so that tool would be only available in a MacOSX vm and I doubt it'd be worth the hassle, esp. since I'd end up having a demosaiced 100mb tif instead of a 20mb raw dng.

Well, there're Windows apps that use DCRAW -- plus DCRAW itself, if you're not afraid of the command line. But that still leaves you with a TIFF instead of a raw DNG, of course.

Quote
But I'm hopeful that in LR's raw processing adjusting the exposure doesn't collide with tone curves either applied manually or via picture styles.

Yes, one would hope so. In the past, I know it was emphatically not the case, but that was many moons ago...no idea if they've fixed it.

It'd be pretty simple to test. Do a three-shot bracket. Apply a corresponding exposure compensation to both the over- and under-exposed shots to normalize them to the middle shot -- that is, if you shot at 0, +1, and -1, then expose for 0, -1, and +1 (precisely by the numbers; don't eyeball it). Then compare all three. If they look identical (except for shadow noise and up to a stop of highlights blowing early), then they've fixed that problem. If there's any visible difference between the three, then they haven't.

Quote
(I)f I understand you correctly you're saying that if the postprocessing software is capable of operating in raw space iso50 should be equal to ettr @iso100?

The data recorded by the sensor (and, presumably, written to the raw file) is identical for ISO 50 and ISO 100; all that's changed is the meter is told to overexpose by a stop and the raw processing engine is told to underexpose by a stop. So, yes, if you use the same shutter and aperture, ISO 50 is the same as ISO 100 with one stop of digital underexposure (again, assuming the digital underexposure is done properly, in the camera's linear raw space before any other adjustments).

(There might be some subtle advantage to doing it in-camera with ISO 50...Chuck Westfall could shed some light on that. But, if there is, the effect would be very, very subtle.)

Cheers,

b&
Title: Re: ISO 50
Post by: Hobby Shooter on January 19, 2013, 08:58:47 PM
so regarding of the subject (motive with no high lights = motive with a small DR) you can overexpose and get a benefit of the over exposure in the shadows

That's great information, thanks! I'll certainly use that once I've got a 6d and am doing tripod macro focus stacks with low dr objects.
I do that regularly with my 5D3 to work around the shadow noise. Results are normally great.

Mikael, question to you, do I understand correct that you mean this is best for low DR pictures ie flatter? I learned through reading a couple of articles to also use this in more high DR situations like taking a street picture with the sun low. I have no experience of not being able to recover details from overexposed highlights. Is there something I'm missing here?
Title: Re: ISO 50
Post by: TrumpetPower! on January 19, 2013, 09:27:16 PM
no they are not
At 100iso  with the same metering the   sensor charge  is under 100 %  and at the read out =before overload and  clipping
with 50iso your double the time  or open up the lens 1 stop and therefore blow one stop of highlight.

As I've mentioned, as far as the sensor is concerned, they are the same. 1/400 @ f/8 @ ISO 100 results in the same raw file as 1/400 @ f/8 @ ISO 50.

The difference is that the meter will read a stop slower and the raw processing engine will apply a stop of digital underexposure to compensate.

But that's all to do with the meter and the post-exposure workflow. The actual exposure of the sensor and what it records is identical.

Similarly, with highlight tone priority turned on, you again get the exact same raw file at 1/400 @ f/8 @ ISO 200/HTP, but the meter reads a stop faster and the raw processing engine applies a stop of digital overexposure. You gain a stop of headroom at the expense of a stop more noise in the shadows -- but, once again, this is all done by starting with the exact same exposure recorded by the sensor, just with shifting meter readings and post-exposure processing metadata instructions.

(Again, all with the caveat that there may be a bit of electronic jiu-jitsu to marginally help achieve slightly better results, and that your raw processing software absolutely must be doing the exposure compensation in the camera's linear raw space before any other adjustments.)

Cheers,

b&
Title: Re: ISO 50
Post by: pwp on January 19, 2013, 11:34:01 PM
50 iso vs ND filters? I think other posters have made it clear that 50 iso is a compromise at the best of times. If your project requires a slowdown, ND is the preferred route.

-PW
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 10:57:04 AM
The sensor does not care about iso, iso step is added after the readout.

Actually, that's not true -- and, presumably, at the heart of your misunderstanding.

Analog electronic (not digital) amplification / gain is applied to all ISO settings above the base ISO. It's like turning up the volume knob on your stereo. The readout is performed after that gain has been applied. And, just as your amplifier will start to produce more and more ugly-sounding distortion the louder and louder you crank that knob, your camera will produce more and more noise the higher you boost the ISO.

ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases. What changes is first the camera's metering system and second the digital (not analog) post-processing. That post-processing is quite simple, really...in the case of ISO 50, all the digital values from the initial sensor readout are exactly halved; with HTP, they're exactly doubled. (And, of course, with ISO 100, they're left as-is.) That's all simple integer math, too -- nothing fancy.

Hope that clarifies things somewhat....

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 12:19:40 PM
the only purpose the sensor has is to collecting photons
agree?

Disagree - it does more.  The photon wells collect photons, there is a lot of additional circuitry on a sensor besides just the photon wells.

TrumpetPower is absolutely correct in his statement that, "ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases." (well, almost correct - the base ISO isn't exactly 100 for all sensors, so even at ISO 100, some gain may be applied - but it is the same gain in all three cases).  He's also correct about ISO 50 being a linear 50% reduction, but incorrect about HTP being a linear doubling (HTP processing is application of a tone curve to boost the shadows and midtones but not the highlights).
 
HTP. it is a halving of infaling light= halving of the amount of charged  electrons= go from 100 to 200 iso and make a head room, the analog signal is different = 100iso and 200 iso
Agree?

Disagree.  When you set ISO 200 with HTP, the camera is actually exposing at ISO 100, which is why ISO 100 cannot be set with HTP on, but (incorrectly) reporting ISO 200 in the metadata and setting the HTP flag.  If you open an HTP RAW file in something like Rawnalyze, you'll see it's a stop underexposed - it's not halving the incoming light, it's reducing the analog gain applied to the same amount of light, by one stop.
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 12:31:25 PM
well then take a look what happening with HTP , 100 iso exposed as a 200iso exposure= under exposed and later adjusted .
not the same signal from the sensor ( and do nor mix apples with bananas this time)

The point is that ISO 50, ISO 100, and HTP ISO 200 are the same analog gain at the sensor, and if the aperture and shutter speed are held constant, the RAW data coming out of the ADC are the same for all three ISO settings.

regarding 50iso and 100 iso= not the same parameters regarding time

You're saying if I set my aperture and shutter in M mode, and then change from ISO 100 to ISO 50, my exposure time or aperture will change?  I'd like to see some evidence for that...
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 12:36:30 PM
Well Neuro, read again what Im answering earlier, Im going to the gym for a hour , we can discuss it later

I don't need to read the same incorrect statements again, thanks.  Enjoy your workout!
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 01:23:45 PM
He's [...] incorrect about HTP being a linear doubling (HTP processing is application of a tone curve to boost the shadows and midtones but not the highlights).

That makes sense -- thanks for the correction. At a rough guess, starting with the original linear data I'd suggest that the HTP curve is still a linear doubling from full dark until the last stop or two of brightness, and then a smooth curve from there back to unity at the saturation point. In Photoshop, create a new curve with one point, 92 as the input and 184 as the output, for an idea of what it might look like. Then apply white balance and color correction matrix and s-curve for contrast and the rest as usual. At least, that's how I'd do it....

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 02:02:14 PM
can you boys read?
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html (http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html)

it is hard  to discuss HTP etc if you do not know what it means

Can you not be insulting, boy?
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 02:15:43 PM
can you boys read?

Yes, we can. Whether you can remains to be demonstrated. From your very link:

Quote
By the way, underexposing at lower ISO is precisely what Canon cameras do in the raw data when Highlight Tone Priority (HTP) is enabled; and what Nikon cameras do when Active D-Lighting (ADL) is enabled. Instead of using the ISO gain set by the user, the camera uses a lower ISO (but exposes with the indicated aperture and shutter speed), effectively underexposing the image; this provides more highlight headroom. In post-processing, the image data can be brought back up while preserving the highlights with a modified tone curve in higher exposure zones. The place where image quality suffers is in shadows at lower ISO, precisely as the above quantitative model predicts.

That's exactly what neuroanatomist and I have been writing all along. Instead of using the ISO gain set by the user (200), the camera uses a lower ISO (100) (but exposes with the indicated aperture and shutter speed). In other words, ISO 200 w/ HTP is exactly the same as ISO 100, but with a different tone curve.

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 02:41:56 PM
No problem admitting when I am wrong.  But I'm not.

You stated:
HTP. it is a halving of infaling light

That's flat out wrong. The light is not being halved, rather, as we and the page you linked correctly state, the gain is being halved, relative to the selected ISO value.

Further, you suggested that setting ISO 50 changes time value and/or aperture...and that's wrong, as well.
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 03:19:45 PM
HTP. it is a halving of infaling light

I think you must study the subject and understand how iso gain works together with full charge and then what it means by 200 iso= halving the number of electrons.

Which are we halving? Light or electrons? Are you going to admit being wrong about the light being halved, or just accuse others of not being able to admit when they're wrong?

Interestingly, I notice that you're consistently ignoring my question about ISO 50 changing aperture/shutter values...

last time I was answering you when you also where totally wrong I was turned off because of my language.it will not happen this time.

Questioning our ability to read, as I stated, is highly insulting, especially the fact that you took the time to edit your post to bold that remark.  It seems you have a history of insulting behavior here, which resulted in past consequences and yet continues. 
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 05:14:09 PM
Once more unto the breach....

The following "Sunny f/16" exposures all result in the exact same amount of analog gain applied to the readout of the sensor, and therefore the exact same raw file:

1/400s @ f/8 @ ISO 50
1/400s @ f/8 @ ISO 100
1/400s @ f/8 @ ISO 200 + HTP

Assuming the camera meter says you're properly exposed for the ISO 100 shot, it'll say you're one stop underexposed for the ISO 50 shot and one stop overexposed for the ISO 200 shot. But, if you ignore the meter and use the same shutter and aperture for all three shots, only changing ISO, you will get the exact same raw file.

...again, with the caveat that the metadata will indicate the ISO you had the camera set to, which will result in one stop of digital (i.e in ACR or DPP or LR or wherever) underexposure for the ISO 50 shot and one stop of digital overexposure for the ISO 200 + HTP shot. That means that, though the raw files are identical for all three, the numerical values recorded in them are divided by 2 for ISO 50 and multiplied by 2 for ISO 200 + HTP before any other processing is done. (It's a linear operation for ISO 50 and a non-linear graduated operation for ISO 200 + HTP.

In contrast, if you were to make the exact same exposure but with ISO 200 without HTP, analog electrical amplification would be applied to the signal before the analog-to-digital converter reads the data, sufficient to double the signal strength. The actual data recorded to the raw file would be different, though it would bear a superficial resemblance to the HTP shot after the initial digital compensation had been applied. Indeed, the regular, non-HTP shot would have more useful dynamic range. Set the ISO to 400 (still without HTP) and even more analog amplification is applied before the ADC digitizes the signal.

There is never a case where the starting point with ISO 50 or ISO 200 + HTP is any different from the exact same shot (same aperture and shutter) at ISO 100. The difference is entirely in the value displayed for the camera's meter and the way the raw file is processed. Any time you shoot with ISO 50 or ISO 200 + HTP, you can do the exact same thing by using the same aperture and shutter as you would at the expanded ISO settings but using ISO 100 instead, and then doing your own digital push or pull in post-processing.

So, why would you want to use either?

If you're shooting JPEGs, ISO 50 is useful when you wish you had a one-stop neutral density filter but you don't.

If you're shooting JPEGs and you care more about the highlights than the shadows -- such as when photographing a bride in a white dress -- HTP will cause the JPEG to render those highlights with more visible detail.

If you're shooting raw and doing ETTR (expose-to-the-right), you're doing the exact same thing as ISO 50. So, you might as well set the camera to ISO 50 and thereby get a preview image on the back of the camera that's closer to your desired final rendering.

If you're shooting raw and you're doing ETTL (expose-to-the-left) in order to capture as much bright detail as possible, you again might as well turn on HTP again to get a more accurate preview.

Lastly, if you're doing a very methodical manual HDR shoot, you might want to consider using ISO 50 for the shadow exposure and HTP for the highlight exposure -- being careful to actually properly adjust the shutter. That is, you might shoot, all at f/8, 1/200s @ ISO 50, 1/400s @ ISO 100, and 1/800s @ ISO 200 + HTP. All three images will be processed internally as if all were shot at ISO 100, but the JPEG previews for all three will be rendered to look very similar. However, the shadows will be cleanest with the ISO 50 shot and there will be more highlight detail with the ISO 200 shot. You could then process them identically in Photoshop and mask in the highlights and shadows from the respective files and get a seamless, natural-looking image with cleaner shadows and more highlight detail. You could, of course, do the exact same thing by shooting them all at ISO 100 and manually applying the digital exposure compensation before layering and masking them in Photoshop.

Cheers,

b&
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 05:54:22 PM
I give up....

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 05:56:51 PM
What is it  you Neuro  and TrumpetPower not understand ?

Well, I'd like to say I don't understand your rudeness and steadfast refusal to admit when you're wrong, but I'm afraid I understand them all too well.

You say read your earlier comments?  Ok.

I read that you stated HTP halves the amount of light.  Do you believe that? 

The data recorded by the sensor (and, presumably, written to the raw file) is identical for ISO 50 and ISO 100; all that's changed is the meter is told to overexpose by a stop and the raw processing engine is told to underexpose by a stop.

no they are not
At 100iso  with the same metering the   sensor charge  is under 100 %  and at the read out =before overload and  clipping
with 50iso your double the time  or open up the lens 1 stop and therefore blow one stop of highlight.

I read that you stated that ISO 50 changes shutter speed or aperture by one stop. Do you believe that?

Neuro
put your camera in front of a white wall, see what you get for values ​​at 100 iso then compare with 50iso
you will find that the exemplel 1/60sec f-5.6 will be with 50iso 1/60 sec f-4, 0 = 1 stop richer exposed compared to 100iso and you lose 1 stop of high light

I'm talking about the RAW file, not the metering.  Unless I change the aperture or shutter, or let the camera do that (in an auto exposure mode like Av or Tv), there will be no difference in the sensor-derived image data between ISO 50 and ISO 100. Both are ISO 100 exposures, tthe ISO 50 data will merely be pulled down a stop by the RAW engine.

As for HTP, it's possible we're saying the same thing in different ways about the what (HTP ISO 200 is actually being underexposed at ISO 100 then brought back up).  But where you seem to be wrong is the when - your contention is apparently that the data are altered on the sensor.  Perhaps I misunderstand you, and you are referring to the actual ISO 100 exposure when ISO 200 is set in camera as that alteration. But what I'm saying, and TrumpetPower is saying, is that the HTP ISO 200 exposure RAW file is the same as an ISO 100 (non HTP) RAW file, and your statement that, "you halve the number of electrons" indicates you believe the RAW file is different. If you mean relative to an actual ISO 200 (non HTP) exposure, fine - but that's not what we've been talking about. 

If you mean ISO 100 RAW is different than HTP ISO 200 RAW, that's wrong, and if you think that's what the page you linked and keep on re-quoting is saying, you're misinterpreting it. It states: "In post-processing, the image data can be brought back up while preserving the highlights with a modified tone curve...."  Post-processing, not the RAW data file, as your statement about halving the number of electrons indicates. There is no change in the number of electrons between ISO 100 and HTP ISO 200, both are ISO 100 exposures, same number of electrons, just handled differently in post.  If you don't understand that, perhaps you should re-read those links of yours.
Title: Re: ISO 50
Post by: Marsu42 on January 20, 2013, 08:00:22 PM
The sensor does not care about iso, iso step is added after the readout.
Actually, that's not true -- and, presumably, at the heart of your misunderstanding.

Thanks for explaining Trumpetpower & Dr. Neuro (which I usually trust to be correct), htp & iso50 aren't self-explanatory and hardly documented anywhere - and in other articles there's still the theory that htp does some magic because it's done inside the image pipeline - probably because no one knows the exact tone curve Canon is applying.
Title: Re: ISO 50
Post by: Don Haines on January 20, 2013, 08:14:36 PM
"Halves the amount of light"? Please correct me if I am wrong..... But there is nothing you can do with sensor settings or camera modes that will change the amount of light.... You can play with gain and linearity and mapping color depths, but the amount of light remains unchanged.  You can change the amount of light with shutter speed, aperture, or slapping on a neutral density filter, but not with the sensor.
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 08:26:57 PM
Thanks for explaining Trumpetpower & Dr. Neuro (which I usually trust to be correct), htp & iso50 aren't self-explanatory and hardly documented anywhere - and in other articles there's still the theory that htp does some magic because it's done inside the image pipeline - probably because no one knows the exact tone curve Canon is applying.

Yep.  Most RAW converters see the HTP flag in the metadata, and apply their version of Canon's tone curve. But some RAW converters ignore the metadata flag (e.g. Rawnalyze) and just show you the 1-stop underexposed image as it's actually recorded in the RAW image data.

Title: Re: ISO 50
Post by: Meh on January 20, 2013, 10:00:01 PM
Oh boy  :o
Title: Re: ISO 50
Post by: Meh on January 20, 2013, 10:56:38 PM
"Halves the amount of light"? Please correct me if I am wrong..... But there is nothing you can do with sensor settings or camera modes that will change the amount of light.... You can play with gain and linearity and mapping color depths, but the amount of light remains unchanged.  You can change the amount of light with shutter speed, aperture, or slapping on a neutral density filter, but not with the sensor.

that is not what Im saying, every iso step =is a halving of the number electroner, the sensor has no knowledge of iso at all, it collects photons  and the number of photons / electrons is determined by time and the light inlet.

That's exactly what you said... "HTP. it is a halving of infaling light" are your exact words.  Even this last statement from you is not even internally consistent.
Title: Re: ISO 50
Post by: TrumpetPower! on January 20, 2013, 11:28:48 PM
that is not what Im saying, every iso step =is a halving of the number electroner, the sensor has no knowledge of iso at all, it collects photons  and the number of photons / electrons is determined by time and the light inlet.

That is an absolutely incorrect statement.

With the now-beaten-to-death exceptions of ISO 50 and HTP, ISO is entirely a function of the sensor. As I've repeatedly attempted to explain, with increasing ISO the sensor applies increasing amounts of analog amplification, and all this happens on the sensor, well before the analog signal is digitized.

Yes, the number of photons that impinge upon the sensor is dependent upon the aperture and shutter (and, of course, the luminance of the scene as projected by the lens). But the number of electrons that reach the analog to digital converter (ADC) depends on how much analog amplification the sensor applies to the readout -- and the amount of amplification is directly set by the user (or the autoexposure system) with the ISO control.

With ISO 50, 100, and 200+HTP, the number of electrons per photon is the same. With ISO 200 (without HTP), thanks to analog amplification, twice as many electrons per photon make it to the ADC. The number of electrons per photon is doubled again with each additional stop of ISO.

(As a side note, "inbetween" ISO settings, those not powers of two times 100 or whatever the base ISO is, are again, with most camera systems, achieved by digital pushing or pulling from the nearest full-stop ISO. ISO 125 produces the same raw file as ISO 100 but with a metadata flag telling the raw processor to add 1/3 stop of digital push, and ISO 160 is really ISO 200 with 1/3 stop digital pull.)

And just, to further clarify what digital versus analog exposure adjustment means...if you were to write a computer program that translated the data in a raw file into a massive spreadsheet, divide every number in the spreadsheet by 2, and then translate from the spreadsheet back to the original raw file format, you'd do exactly the same thing that ISO 50 does. If you were to translate ISO 50, ISO 100, and ISO 200+HTP (assuming identical scenes, apertures, and shutter speeds) files each into separate spreadsheets, they'd all have the exact same numbers in them. But, if you exposed at ISO 200 (without HTP, but still keeping the shutter and aperture and everything else the same), the numbers in your spreadsheet would be twice as big...but they'd also have a higher standard deviation, indicating additional noise due to the distortion from the higher analog gain applied to the sensor readout. If you then, say, made the shutter a stop faster, the ISO 200 numbers would be back in line with the ISO 100 numbers, but you'd still have a higher standard deviation because of the additional noise from the increased analog amplification.

I really don't know how to express this any more clearly. If you still don't understand, then perhaps you should explain how you think the whole shebang actually functions, rather than just vaguely handwave about photons and electrons with unspecific and irrelevant references to Web pages that actually describe things correctly, and the opposite of what you describe.

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 20, 2013, 11:42:55 PM
that is not what Im saying...the sensor has no knowledge of iso at all, it collects photons  and the number of photons / electrons is determined by time and the light inlet.

...and apparently, by the HTP setting as well, which reduces by half the number of photons reaching the sensor.  Or so you stated earlier, in multiple posts and more than one way:

HTP, here you have exposed the motive 1 stop shorter, halving the number of photons and you get a High light head room and then another curve is  applied with a lift in lower areas/levels and a softer curve at the top / high lights
Here 100iso are exposed as i where  200iso  which means 1 stop shorter exposure , the sensor collect less photons who are converted  in to a charge/signal.

HTP. it is a halving of infaling light

Do you stand by those assertions, Mikael?  ::)

That's exactly what you said... "HTP. it is a halving of infaling light" are your exact words.  Even this last statement from you is not even internally consistent.

Factual consistency does not seem to be one of Mikael's strong suits...  But in other ways, he's quite consistent - his use of bold text, his derogatory questioning of others' understanding coupled with urging others to 'read' and 'try to understand', his repetition of the same statements in post after post, in these and similar areas, he seems consistent to the point of boredom.
Title: Re: ISO 50
Post by: Meh on January 20, 2013, 11:52:05 PM
With the now-beaten-to-death exceptions of ISO 50 and HTP, ISO is entirely a function of the sensor. As I've repeatedly attempted to explain, with increasing ISO the sensor applies increasing amounts of analog amplification, and all this happens on the sensor, well before the analog signal is digitized.

Yes and no, depends how you define the "sensor".  It could be that this is a fine semantic point.  There is a lot of circuitry on the same chip but does that make it part of the "sensor"?  If the ADC were to be fully integrated onto the same chip is that part of the "sensor"?  What about memory?

So, it is imperative then that we define what we mean by "sensor" and discuss based on a common definition.  In my view, it is most practical to refer to the sensor as the "light/electron gathering" parts.  Including much more than that gets right into the quagmire I described above.

The amount of light incident on the sensor is NEVER a function of ISO.  It is only a function of aperture and shutter speed.  ISO gain is applied after the exposure.  The so-called analog gain is applied prior to readout but that is only up to some point (something like ISO 1600?)  beyond which it is applied digitally after readout.

So, the statement that "ISO is entirely a function of the sensor" might be somewhat correct depending on how we define "sensor" but only up to about ISO 1600.
Title: Re: ISO 50
Post by: Meh on January 20, 2013, 11:59:33 PM
Factual consistency does not seem to be one of Mikael's strong suits...  But in other ways, he's quite consistent - his use of bold text, his derogatory questioning of others' understanding coupled with urging others to 'read' and 'try to understand', his repetition of the same statements in post after post, in these and similar areas, he seems consistent to the point of boredom.

Michael IS a very rude boy indeed.
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 12:10:37 AM
The so-called analog gain is applied prior to readout[. . . .]

Because the readout is the point where the signal logically leaves the sensor, it should be self-apparent that analog gain must be applied by the sensor itself to the signal before (or as) it is read out.

You're of course correct that expanded high ISOs are again digital simulations and not analog processes, but I suspect your cutoff of ISO 1600 only applies to very old cameras. I may be mistraken, but I'm pretty sure that digital ISO boost only happens with expanded ISO settings. With the 5DIII, native (analog) ISO should extend all the way to ISO 25,600...but I wouldn't bet more than a cup of coffee on that exact number.

Cheers,

b&
Title: Re: ISO 50
Post by: rpt on January 21, 2013, 12:23:02 AM
"Halves the amount of light"? Please correct me if I am wrong..... But there is nothing you can do with sensor settings or camera modes that will change the amount of light.... You can play with gain and linearity and mapping color depths, but the amount of light remains unchanged.  You can change the amount of light with shutter speed, aperture, or slapping on a neutral density filter, but not with the sensor.
Obviously a number of us are clueless. HTP stands for Half The Photons! Now how that happens in the sensor needs to be discovered...

And oh, just in case somebody takes my post at face value, here is the tag:
<SARCASM/>
 ;)
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 12:24:25 AM
Because the readout is the point where the signal logically leaves the sensor, it should be self-apparent that analog gain must be applied by the sensor itself to the signal before (or as) it is read out.

Depends when, where, and how that "analog gain" is being applied and on what we think is the beginning of the read out process.  My suggestion is that we think of the "sensor" as the photo-sensitive material and the electron wells.  Everything after that is electronics and should be considered as part of the read-out circuitry including the analog gain.  Applying the analog gain is not part of the exposure per se and, it adds noise which by the usual definition is part of the read-out noise (if we agree on two categories of noise those being photon shot-noise and read-out noise).
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 12:25:29 AM
"Halves the amount of light"? Please correct me if I am wrong..... But there is nothing you can do with sensor settings or camera modes that will change the amount of light.... You can play with gain and linearity and mapping color depths, but the amount of light remains unchanged.  You can change the amount of light with shutter speed, aperture, or slapping on a neutral density filter, but not with the sensor.
Obviously a number of us are clueless. HTP stands for Half The Photons! Now how that happens in the sensor needs to be discovered...

And oh, just in case somebody takes my post at face value, here is the tag:
<SARCASM/>
 ;)

Absolute. Best. Response.
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 12:32:43 AM
I suspect your cutoff of ISO 1600 only applies to very old cameras. I may be mistraken, but I'm pretty sure that digital ISO boost only happens with expanded ISO settings.

The highest ISO setting that is based on analog gain is certainly going to be different among bodies and may have increased with the latest tech but it's not my understanding that digital gain is only with expanded ISO settings.  However, I'm no expert... Neuro?
Title: Re: ISO 50
Post by: friedmud on January 21, 2013, 12:32:58 AM
ISO 50 is a complicated subject... and really depends on the nature of the sensor in your particular camera.

The following is something I posted over at Nikon Rumors in response to seeing someone say that ISO 50 was underexposing and then correcting:

(EDIT: I just want to be clear that his was in a discussion about landscape photography, where an aperture has been chosen for DoF and sharpness and the shutter speed is ranging to get the exposure right)

"Firstly, it's not "underexposing then correcting in software"... that's more of what happens with things like "Active-DLighting" and "Highlight Tone Priority" (on the Canon side) or using very high ISO. If anything, ISO less than 100 _overexposes_ and then pulls back in software. If you fix aperture and you expose at ISO 100 and get 1 second exposure... Then you drop ISO to 50 and take the same shot the shutter time will be 2 seconds. If the sensor can't be "less sensitive" than ISO 100 then you are overcooking the sensor (ie, overexposing). The camera can then correct in software to give you the correct looking exposure (possibly at the expense of highlights that might have been blown out and can't be recovered). Because of this there can be a small drop in dynamic range (you might have lost some highlights).

A few thing about this:

1. Physics means that an ISO 50 shot will definitely include the effects of more photons striking the sensor. That will reduce "random shot noise" which can give you a visible reduction in noise. I have done tests with my D600 and there is less noise at ISO 50,

2. At the worst case of a sensor that really can't go below ISO 100 at all, this process is equivalent to overexposing by one stop and pulling back your RAW file in post. Essentially it is equivalent to Exposing To The Right (ETTR http://en.wikipedia.org/wiki/Exposing_to_the_right (http://en.wikipedia.org/wiki/Exposing_to_the_right))... Which, in scenes of lower dynamic range can give you a tangible benefit of having less noise in the shadow areas. So once again we might be shaving off noise.

3. How much highlight you lose is very sensor dependent. The D600 has a lot of headroom in this area and if you look at DXOMark ( http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Database/Nikon/D600 (http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Database/Nikon/D600) ) it doesn't show a loss in Dynamic Range when going to ISO 50.... just that it doesn't gain much either.


In summary: be careful about spreading dogma like this. Every sensor / camera is different. In particular, I have done my own testing on the D600 and have found the tradeoff for lower noise to dynamic range to be more than acceptable. In extreme dynamic range scenes I may choose 100 to just be safe... but in all of my shooting with the D600 so far ISO 50 has produced better (less noise with the same / similar dynamic range) photos.

Everyone: don't just take my word for it (or anyone else on the internet) there is no reason not to do these types of tests with your own gear. One of the first things I do when I receive any new piece of gear is test it's limits. Not to be dissappointed but to know where they are so I can make correct decisions about tradeoffs in the field..."
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 12:47:40 AM
@friedmud... what you are describing is the effect of increasing the length of the exposure (from 1 second to 2 seconds in your example) and it's that real increase in the number of collected photos that improves the SNR not any magical effect of using ISO50.

But you're statement that "ISO50 is not underexposing then correcting" is absolutely correct because ISO50 is overexposing (relative to ISO100) then correcting.
Title: Re: ISO 50
Post by: friedmud on January 21, 2013, 12:59:10 AM
Once more unto the breach....

The following "Sunny f/16" exposures all result in the exact same amount of analog gain applied to the readout of the sensor, and therefore the exact same raw file:

1/400s @ f/8 @ ISO 50
1/400s @ f/8 @ ISO 100
1/400s @ f/8 @ ISO 200 + HTP

Hey Trumpet, I don't want to get pedantic (because you are mostly right in what you are saying, and you're trying to provide clarity to someone who is definitely wrong) BUT... I feel like since we've had a good technical discussion here I should point out that you have to be careful about that "exact" word you used there.

Your statement is only "exactly" right if a sensor's "base ISO" is exactly 100.  For many modern sensors it is close, but even a 5DMk3 is closer to 80 and it appears as though a Nikon D800 is closer to 75.  What this means is that there is some analog gain applied, even at ISO 100... and there will be different analog gain applied at 50.

What this means is that shooting at 50 might not lose you a full stop of highlights.  Indeed, shooting at ISO 75 on a D800 won't lose you any highlights at all (compared to ISO 100) and you get the added benefits of more photons (ie, less noise).

Sorry to be pedantic... I don't want to derail what you're saying.... I just want people to realize that not everything about a camera sensor is set in stone by a god somewhere... and each and every sensor type has it's own unique aspects... :-)
Title: Re: ISO 50
Post by: friedmud on January 21, 2013, 01:02:58 AM
@friedmud... what you are describing is the effect of increasing the length of the exposure (from 1 second to 2 seconds in your example) and it's that real increase in the number of collected photos that improves the SNR not any magical effect of using ISO50.

Oh, I agree (with my quibble above about understanding the effect of "base ISO").  I apologize for reposting that here out of context... it was simply more convenient than retyping it :-)

The context was landscape photography... and I was trying to explain why I shoot at ISO 50 sometimes (because of less noise from the longer exposure... well, along with any other reasons why a longer exposure might be wanted, like blurring a waterfall).
Title: Re: ISO 50
Post by: Aglet on January 21, 2013, 01:08:58 AM
clip..
1... I have done tests with my D600 and there is less noise at ISO 50,..

Whoa, stop the presses.
your D600 has noise?!?...
That's a distinctly Canon issue. ;)

BTW, sounds like most of the ISO-arguing around 50-100-HTP and D-L know enough about how to USE it.

@neuro, @trumpet, @ etc...
don't forget @michael seems to speak english as a 2nd language so I often find his sentence syntax confusing but after wasting time reading nearly 3 pages of arguments from you all it seems to me you're perfectly aware how this technology works but can't seem to see that for the scrap that's broken out over semantics and typos.

I initially thot I'd make more use of iso 50 on my 5D2 at some point for making cleaner low key shots.  Turns out I rarely shoot anything like that to advantage.

I DID get out for an hour of photo-therapy around sunset on Saturday, a nice way to deal with too much stress from work and family.
Shot with 5d2, d800, d5100s and a Q.  The first 2 were equipped with 70-200mm zooms and I was shooting the same high key scene in dim overcast skies and snow everywhere, including inside my car cuz it was too cold to step outside of it.
I liked shooting the 5d2 w 70-200/2.8L is2
I loved shooting the d800w 70-200/4 vr3, crisp handling, spot-on WB, better AF in blowing snow; a condition that often had my Canon cameras failing to AF properly all too often.
D5100s AF'd well but gave me some odd WB, often a bit green but easy to fix in post.

Everybody, get out and shoot more! :)
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 01:17:36 AM
Nice thread. Learning a lot.

I think this evening I will take two shots with ISO 50 and 100 and post them here for us to see and learn.
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 07:10:55 AM
That's exactly what you said... "HTP. it is a halving of infaling light" are your exact words.  Even this last statement from you is not even internally consistent.
no I said by using HTP it is like underexpose  1 stop, go away from 100iso  by an under exposure which well be equal to a 200iso exposure   and thereby make a head room=  which later can compensates with gain and curves

Really?  You didn't say, "HTP. it is a halving of infaling light," and you're sure about that??

Let's check.  You said:

HTP, here you have exposed the motive 1 stop shorter, halving the number of photons and you get a High light head room and then another curve is  applied with a lift in lower areas/levels and a softer curve at the top / high lights
Here 100iso are exposed as i where  200iso  which means 1 stop shorter exposure , the sensor collect less photons who are converted  in to a charge/signal.

...and you then said:

HTP. it is a halving of infaling light

Sure, you also talked about HTP underexposing by a stop.  But for you to deny claiming the light was halved is stubborn intransigence, and a complete lie...a particularly foolish one, too, given that your previous statement that you deny making is there for all to read, and easily catch you in your transparent lie of denial.  The second one, "HTP. it is a halving of infaling light," I could accept as linguistic confusion...but it followed the earlier statement where you talk about halving the number of photons, the sensor collecting less photons, and a 1-stop shorter exposure being used, all as a description about how HTP achieves the highlight recovery. That's not linguistic semantics and typos as Aglet suggests, that a very concise, understandable description where it's quite clear what you mean...it's just WRONG.

But...not only can you not admit being wrong, you deny you even made the statements quoted above.

Moreover, you also stated:

You Neuro and others seems to have a very hard time  to admit that you are wrong .


It is manifestly clear that YOU are the one unable to admit when he is wrong.

At least you were right about one thing:

it is hard  to discuss HTP etc if you do not know what it means

You are obviously having a hard time discussing HTP, because while you appear to understand the consequences in terms of highlight recovery and increased shadow noise (or at least, you can parrot the statements of others who understand that), you haven't got a clue about the image data manipulations that underlie HTP, as clearly shown by your flat out wrong description of a shorter exposure leading to halving the incident light for the exposure. 
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 07:39:38 AM
Your statement is only "exactly" right if a sensor's "base ISO" is exactly 100.  For many modern sensors it is close, but even a 5DMk3 is closer to 80 and it appears as though a Nikon D800 is closer to 75.  What this means is that there is some analog gain applied, even at ISO 100... and there will be different analog gain applied at 50.

Sorry to be pedantic... I don't want to derail what you're saying.... I just want people to realize that not everything about a camera sensor is set in stone by a god somewhere... and each and every sensor type has it's own unique aspects... :-)

Sorry, friedmud...you're late to the proverbial pedantic party...my own pedantry preceded yours by about 37 posts...  ;)

TrumpetPower is absolutely correct in his statement that, "ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases." (well, almost correct - the base ISO isn't exactly 100 for all sensors, so even at ISO 100, some gain may be applied - but it is the same gain in all three cases).
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 08:01:06 AM
My test.
1. It is unscientific, do not pounce on me. Am learning!
2. Stats: 1dx. 24-70 II. Manual focus, exposure, WB (tungston). f5.6 1/4 and 1/8.

Its all for us to see, but to my eyes:
1. The tint at ISO 50 is truer. (This is next to my desk and I can make a visual comparison)
2. The blown whites between the statue and lamp is blown more on 50 ISO.
3. 50 ISO shows marginal noise and sharpness improvement. (This could of course be just my eyes playing games.) Or is there a shake? I did use a sturdy tripod.

Do you think I should make another test? If yes, how should I improve? :)

Thank you.

Sanjay
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 08:15:46 AM
In HTP  the sensor  has now been hit by  less light/photons
(http://audibleconnection.com/wp-content/uploads/2011/08/smiley-bangheadonwall-yellow.gif)

Like I said, clueless.
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 09:01:56 AM
It should be more blown out, 50 iso is 100 iso over exposed 1 stop= 1 stop earlier clipping in highlights

Sir do not understand. Am not disputing, just unclear as to what you saying. Could you please expand?
Title: Re: ISO 50
Post by: TexasBadger on January 21, 2013, 09:27:10 AM
If you stare at the sun (not recommended) with and without sunglasses it will not seem as bright with the sunglasses.  However, the amount of light reaching you has not changed.  The effect the sunglasses have on the light reaching your retina is similar to using a neutral density filter.  The intensity of the light (measured in photons) has not changed anywhere except for the amount of light hitting your retina (sensor).  Each pixel on the sensor collects fotons like a bucket.  When the bucket is full it cannot hold any more photons.  This is why we get clipping.  Please keep in mind that all of this is not linear but logarithmic.  In film we called it reciprocity failure.  The loss in efficiency was caused by the physical properties of the emulsion.  In digital, the sensor creates heat which has a negative effect in the efficiency.  Any time you increase the ISO, you amplify the entire signal which causes the noise as well as the light values to be increased.  Since a sensor will always have a noise component, the digital processing of the analog scene can be addresses by the digital processing of the information comming from the sensor.  That is why apparent noise can be reduced by software/firmware.  The 5D3 has much better noise reduction than the 5D2, even though the sensor is essentially the same.  This was achieved by better firmware processing the information coming from the sensor.  You can also reduce the apparent noise by improving the sensor by reducing the signal noise going to the digital processor.  Another caveat is that the smaller the pixel is, the more noise with all other factors remaining equal.

The bottom line is that the ISO is changed for one of two reasons.  The first is to change the aperature/shutter speed combination for the image capture.  The second is for desired effect that noise will have on the resulting captured image.

If you have ever pulled film you overexposed the image and underdeveloped the film.  However, if you pulled Tri-X, you might expose the image for ISO 125 ~2 stop pull and then decreased the development time by 20%.  Remember this is logarithmic not linear.  The purpose of pulling film is to increase the grey scale in the image for more depth and richness in the final print.

ISO 50 is similar to pull processing.  You are overexposing and digitally underdeveloping.  Pulled film will have less dynamic range and or contrast than film not pulled.  You only pull film because you are wanting to increase the grey scale in the resulting image.  You shoot at ISO 50 for the same reason.  Shooting to the right is another way to manipulate the resulting image.

The reality is that you use different ISO values based on the desired resulting image capture.  This is similar to using different types of film in the analog world.  Increasing the ISO changes the amplification of the signal from the sensor.  It also increases the contrast and the noise.  Increasing the speed of your film increases contrast and grain. Grain is the analog equivalent of noise in digital.  The reason that faster film was more grainy was that the silver crystals in the emulsion were larger which allowed for shorter exposures with increased grain being the trade-off.

Remember that there are still only three components to a proper exposure.  Shutter speed, aperature and ISO.  The art is in the composition and exposure decisions we make.

Now the equivalent of pushing film in the digital arena ...
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 09:29:24 AM
50iso is no 50 iso, it is equivalent to 100 iso over exposed 1 stop, what you gain is for example  slower exposure time which can be handy , running water etc but at the same time that the sensor is richer exposed you lose 1 stop of DR and that is in the highest levels= earlier clipping

Thank you for the explanation. To me, when I re examine the photos based on what you saying, it seems like ONLY the whites are getting overexposed, NOT the entire frame. Could I conclude that not the entire frame but only the whites get over exposed?
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 09:46:19 AM
My 5dmk2 starts at 200 iso if  I enable HTP= 1 stop under 100iso= let fewer photons hit the sensor

Why are you perseverating on this?  Please explain: when the HTP is enabled and ISO 200 is set, the camera is actually exposing at ISO 100...how does that in any way alter the number of photons hitting the sensor?  You seem completely unable to comprehend the simple facts. 

Try to read and study carefully all those other pages you linked earlier.  Let's take it by steps:


What part of the above do you not understand?  In particular, you seem unable to grasp the 3rd bullet point.

It's not complex, yet you fail to understand or acknowledge your errors in comprehension.
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 09:47:26 AM
Here is another picture that helps me understand this better.
I had shot this on 5d2 just when I was starting off with photography and I used to often wonder why certain portions of the clouds lacked detail. I hunted this photo down in an old HD and yes, it is shot at ISO 50.
Hmmm I too will now avoid ISO 50...
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 09:49:24 AM
There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.

Neuro, my tests indicate differently to this. Iso 50 highlights are clearly more blown. I can never contradict you, so please tell where I am going wrong here..
Title: Re: ISO 50
Post by: TheSuede on January 21, 2013, 09:52:28 AM
The sensor does not care about iso, iso step is added after the readout.

Actually, that's not true -- and, presumably, at the heart of your misunderstanding.

Analog electronic (not digital) amplification / gain is applied to all ISO settings above the base ISO. It's like turning up the volume knob on your stereo. The readout is performed after that gain has been applied. And, just as your amplifier will start to produce more and more ugly-sounding distortion the louder and louder you crank that knob, your camera will produce more and more noise the higher you boost the ISO.

ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases. What changes is first the camera's metering system and second the digital (not analog) post-processing. That post-processing is quite simple, really...in the case of ISO 50, all the digital values from the initial sensor readout are exactly halved; with HTP, they're exactly doubled. (And, of course, with ISO 100, they're left as-is.) That's all simple integer math, too -- nothing fancy.

Hope that clarifies things somewhat....

Cheers,

b&

Well, this was a long thread, and there's to little time...
I'll take this post from the start of the thread and start there. If I missed something in the in-between pages, shoot me! :)

I'm KIND of reading this as you're talking past each other, but anyway:
No, the ISO amplification is added after what is usually called the "read-out". The readout in itself is the analog coupling between the individual pixel charge storage where the charge is translated into a feed line voltage via the cell capacitance, a resistor and the reference level - one of the base definitions of a CMOS sensor.

The conversion from charge to voltage at pixel level is done at a fixed rate, that can only be adjusted by changing the pre-charge or the reference voltage feed, and you usually don't do that. Some machine vision sensors have facilities for this (absolute conversion rate calibration), but no sensors in the commercial area AFAIK. After this conversion has been done, the voltage is "transported" - shorted, connected to - a voltage  amplifier that sits at the edge of the sensor, just before the signal leaves the sensor plate. The ISO amplifier.

In a Canon sensor, you usually have somewhere between 4-12 communication lines out from the sensor plate edge - each of those has it's own voltage amplifier where the ISO gain is applied. This is also what causes most of the vertical banding - the gain in those amplifiers aren't matched perfectly.

At base ISO, the "whites" are in the green channel usually quite close to the absolute clipping point of the individual pixel - the full well capacity. As you approach FWC, no more charges can be stored, no more voltage can be read out from the pixel. At this point, it doesn't matter if you try to lower the ISO amplifier gain, the data is still just a flatline, pinned at the maximum value of the pixel. Like trying to salvage a pure blown white in a jpg file - it's quite impossible.

So what would really be good to know if you're shooting raw is if the maximum pixel voltage that you can convert into an ADU value increases when shooting at one step below "normal" base ISO. And usually it does - by some 5%. The 5Dmk3 goes from about 67ke- to 70-71ke- The added range is mostly compression effects, distorted data - but that doesn't matter much in the highlights. On the other hand, 5% doesn't matter much anyway - +5% is the same as 0.07Ev or 1/14 Ev. Not much.
............

I have no idea how Canons HTP works in the transition from base ISO to higher ISO in newer cameras. If the camera is at ISO400, it's simple - just tell it to halve analog amplification (to ISO200) and compensate in post, pulling in the highlights as you do. In this case you don't lower the actual photometric exposure, you just adjust the amplification. The actual photoelectric conversion rate is constant.

But at base ISO this is meaningless, since there's no data to pull in. The pixels themselves are what they are, they can't send the amplifier any higher voltages, FWC sets the upper limit. Trying to lower amplification in that case is counterproductive, you're just hurting the shadow tone resolution.

compare it to an analog sound chain.
You have a microphone that can convert sound into a voltage, maximum output is 2v. This is the pixel.
You have an amplifier that can amplify the signal if needed (ISO gain, this is NOT in the pixel)
You have a loudspeaker that needs exactly 2v to play at the sound pressure that you want, no more and no less (your image brightness)

You adjust sound pressure at the output - image brightness - by adjusting the amplifier

Now if the microphone gives those maximum 2v from a 96dB sound pressure, screaming into the microphone at 102dB won't increase the maximum output. It will just distort the sound, by clipping. It doesn't matter if you turn the amplifier down, the distortion (clipping) is still there, since it's present at the source, the input of the amplifier. And there's nothing you can do about it except get another microphone with a lower base sensitivity (lower base ISO).

Actually it's quite easy to test - point a camera at something with graded highlight, take one shot at base ISO and one shot with exactly the same shutter speed and aperture at the faked ISO. Try to pull in the highlights in the raw file. Is there any difference?
If there's no difference, you could just as well have shot at base ISO with -1Ev compensation. You're just adjusting if you want to clip the highlight or the shadows, you gain absolutely nothing. It's a 1:1 trade-off.
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 09:52:37 AM
50iso is no 50 iso, it is equivalent to 100 iso over exposed 1 stop, what you gain is for example  slower exposure time which can be handy , running water etc but at the same time that the sensor is richer exposed you lose 1 stop of DR and that is in the highest levels= earlier clipping

Thank you for the explanation. To me, when I re examine the photos based on what you saying, it seems like ONLY the whites are getting overexposed, NOT the entire frame. Could I conclude that not the entire frame but only the whites get over exposed?

sanj, I would strongly recommend ignoring everything Mikael is writing in this thread. He's very, very worng.

If you shoot with the same aperture and shutter at both ISO 50 and ISO 100, you will get the exact same raw file. When you open it in Lightroom (or wherever), it's starting with the same raw data, but it sees the ISO metatags are different and so, before doing anything else to the image data, it divides all the numbers in the ISO 50 shot by 2.

When you set ISO 50 on the camera, it tells the meter to change by one stop, so the common workflow would be to expose the ISO 50 shot one stop brighter. When you then open it, Lightroom first divides all the values by 2, which gives you the appearance of a file that looks properly exposed. But it wasn't actually exposed at ISO 50, which doesn't actually exist in the camera; it was really exposed at ISO 100. And, just as if you had actually exposed it at ISO 100 and applied one stop of darker exposure compensation in Lightroom, you'd discover you had lost one stop of highlights, you always lose one stop of highlights with ISO 50.

Cheers,

b&
Title: Re: ISO 50
Post by: TexasBadger on January 21, 2013, 09:54:56 AM

Mikael you are missing the point.  Changing film speed is similar to changing the signal amplification +/- in the digital world.  The analogy is that signal amplification is the digital equivalent of changing the crystal size in the films emulsion.  What I am demonstrating here is that the physics of film and digital hasn't changed.  Just think of the light sensitive crystals in the film emulsion as the analog equivalent of light sensitive pixels in the sensor.

The digital sensor is the equivalent of film.  The amplification of the digital signal is the equivalent of the silver crystal size in the film's emulsion.  Shooting at ISO 50 is the equivalent of pulling film.  Shooting at high ISO is the equivalent of pushing film.
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 10:00:33 AM
TheSuede, thanks for the details and corrections on the workings of the electronics!

b&
Title: Re: ISO 50
Post by: TheSuede on January 21, 2013, 10:03:39 AM
sanj, I would strongly recommend ignoring everything Mikael is writing in this thread. He's very, very worng.

If you shoot with the same aperture and shutter at both ISO 50 and ISO 100, you will get the exact same raw file. When you open it in Lightroom (or wherever), it's starting with the same raw data, but it sees the ISO metatags are different and so, before doing anything else to the image data, it divides all the numbers in the ISO 50 shot by 2.

When you set ISO 50 on the camera, it tells the meter to change by one stop, so the common workflow would be to expose the ISO 50 shot one stop brighter. When you then open it, Lightroom first divides all the values by 2, which gives you the appearance of a file that looks properly exposed. But it wasn't actually exposed at ISO 50, which doesn't actually exist in the camera; it was really exposed at ISO 100. And, just as if you had actually exposed it at ISO 100 and applied one stop of darker exposure compensation in Lightroom, you'd discover you had lost one stop of highlights, you always lose one stop of highlights with ISO 50.

Cheers,

b&

Well, isn't that exactly what he's saying?

If you let the camera chose exposure, it will overexpose the raw file, clip more highlights - if you set ISO50.

If you expose manually - same shutter speed, same aperture - the ISO50 and the ISO100 raw files will be almost exactly identical. I don't see where your statements clash in any way.

The main difference is in in-camera jpg, since the in-camera jpg engine usually never uses all the raw data all the way up to blown white. I think the in-camera jpg actually gains something when going to ISO50 from ISO100, but that comes from a different development setting - not better base data.
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 10:14:15 AM
Neuro is wrong about 50iso not you.

No, you are wrong about me being wrong.  You often seem completely unable to distinguish between changing aperture and/or shutter speed, which change the actual amount of light reaching the sensor, and changing ISO, which changes only what the sensor does with the light that falls on it, but has no effect on the amount of that light. For someone who professes to understand the principles of photography, that's a key point - one that seems beyond your comprehension.

There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.

Neuro, my tests indicate differently to this. Iso 50 highlights are clearly more blown. I can never contradict you, so please tell where I am going wrong here..

You're not contradicting me at all, and we are both correct.  What I stated was, 1) there is no benefit to ISO 50 and, 2) if a highlight is already blown at ISO 100, using ISO 50 won't help.  Both of those are true (despite Mikael's seeming inability to comprehend them).  What you're showing simply goes further - not only can ISO 50 not save highlights that would be blown at ISO 100, it can actually cause highlights to blow that would not have blown at ISO 100. 

My point was in reference to using ISO 50 and ISO 100 at the same aperture/shutter speed - in that case, there's no difference in the highlights in the RAW image files, and ISO 50 would not blow any more highlights (the meter would show a stop of underexposure). In your example, you are talking about changing aperture or shutter speed when going from ISO 100 to ISO 50 to maintain a metered exposure. It's that change in aperture/shutter that's causing the blown highlights, not setting ISO 50, per se.
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 10:23:49 AM
Mikael, let's try to make this even more simple.

Consider that you've got four cameras and one tripod set up in a studio. All four cameras are 5DIIIs, and all four have 50mm f/1.4 lenses attached. The tripod is fixed and the lighting (continuous, not flash, just to keep things simple), is held constant. All we're doing is swapping out cameras, focussing on the same spot, and releasing the shutter.

All four cameras are set in manual mode to record to raw (no JPEG), with the following settings:

Camera A: 1/100s @ f/8 @ ISO 50
Camera B: 1/100s @ f/8 @ ISO 100
Camera C: 1/100s @ f/8 @ ISO 125
Camera D: 1/100s @ f/8 @ ISO 200 + HTP

If you then examine each of the four raw files, you will find that the only difference is in the metadata.

Now, we shoot as follows:

Camera A: 1/200s @ f/8 @ ISO 50
Camera B: 1/100s @ f/8 @ ISO 100
Camera C: 1/80s @ f/8 @ ISO 160
Camera D: 1/50s @ f/8 @ ISO 200 + HTP

What we now discover is that each raw file is different.

Let's assume that there was a gray card in the scene. And let's pick a completely arbitrary number of 100 to indicate the average pixel value of that gray card in the 1/100s @ f/8 @ ISO 100 exposure.

What we discover is the following values for that gray card in each of the raw files:

Camera A: 1/100s @ f/8 @ ISO 50: 100
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/100s @ f/8 @ ISO 125: 100
Camera D: 1/100s @ f/8 @ ISO 200 + HTP: 100

Camera A: 1/200s @ f/8 @ ISO 50: 50
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/80s @ f/8 @ ISO 160: 125
Camera D: 1/50s @ f/8 @ ISO 200 + HTP: 200

Now, we're going to try another experiment, shooting the last series, but all at ISO 100. This is what we get:

Camera A: 1/200s @ f/8 @ ISO 100: 50
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/80s @ f/8 @ ISO 100: 125
Camera D: 1/50s @ f/8 @ ISO 100 + HTP: 200

Finally, we're going to do one last pair of experiments with a different set of ISO values. Here're the results:

Camera A: 1/100s @ f/8 @ ISO 100: 100
Camera B: 1/100s @ f/8 @ ISO 200 (no HTP): 200
Camera C: 1/100s @ f/8 @ ISO 400: 400
Camera D: 1/100s @ f/8 @ ISO 800: 800

Camera A: 1/100s @ f/8 @ ISO 100: 100
Camera B: 1/200s @ f/8 @ ISO 200: 100
Camera C: 1/400s @ f/8 @ ISO 400: 100
Camera D: 1/800s @ f/8 @ ISO 800: 100

If that doesn't clear it up, nothing will....

Cheers,

b&
Title: Re: ISO 50
Post by: rs on January 21, 2013, 10:29:54 AM
This is the best entertainment I've had in ages ;D
Title: Re: ISO 50
Post by: rpt on January 21, 2013, 10:30:57 AM
This is the best entertainment I've had in ages ;D
LOL!
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 10:32:00 AM
i have been writing about shutter speed/ f-stops read back

You have been writing about HTP affecting the amount of light that hits the sensor, read back.

If you spew enough drivel throw enough darts, some are bound to hit the target.
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 10:32:48 AM
Well, isn't that exactly what he's saying?

He's been saying many different things regarding ISO50 and HTP, some correct and some incorrect.  He's been particularly wrong about HTP.  It turned into an argument due to some rather rude and insulting comments.
Title: Re: ISO 50
Post by: TheSuede on January 21, 2013, 10:40:52 AM
"Even" I misuse the word 'exposure' very often. I guess this stems from have to many discussions with people that have no real interest in (or meaningful use of) the correct usage.

Try having a conversation with a reviewer or even a seasoned photographer - or a surveillance camera client - and do on all matters use the word 'exposure' correctly. It will confuse them to the brink of insanity :)

The only photographers that I know that actually grasp the meaning of the word 'exposure' are people old enough (or interested enough) to have experimented with and compared results with different film types and development push/pull schemes on several different base formats (135, MF, large format). They know the importance of the separation of exposure and brightness.

The only other two groups I know of that use it correctly are astrophotographers and people with some kind of electroptics degree (and even the people in the camera base module development department often get befuddled when they discuss the resulting images rather than the process in itself).

The important part where you're talking straight past each other seems to be this:
If you let the camera chose exposure, it will overexpose in ISO50
In manual exposure mode it makes no or very little difference between ISO50 and ISO100
None of you seem to disagree on this, so I fail to see the problem.
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 10:46:23 AM
Here is the dumbest question in the thread, but since I am the one that made the test, could I please ask what is HTP?
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 10:48:18 AM
The important part where you're talking straight past each other seems to be this:
If you let the camera chose exposure, it will overexpose in ISO50
In manual exposure mode it makes no or very little difference between ISO50 and ISO100
None of you seem to disagree on this, so I fail to see the problem.

TheSuede, your two-line summary is correct (if, naturally, a bit oversimplified), but that's not what Mikael has been writing. And when neuroanatomist and I have been writing that, Mikael has been arguing that we're worng.

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 10:50:48 AM
My point was in reference to using ISO 50 and ISO 100 at the same aperture/shutter speed - in that case, there's no difference in the highlights in the RAW image files, and ISO 50 would not blow any more highlights (the meter would show a stop of underexposure). In your example, you are talking about changing aperture or shutter speed when going from ISO 100 to ISO 50 to maintain a metered exposure. It's that change in aperture/shutter that's causing the blown highlights, not setting ISO 50, per se.

@sanj - the reason this is relevant, at least to me, is that many times (usually, in fact), I choose aperture and shutter speed for a reason. Aperture is chosen for the desired DoF so I can include/exclude what I want to be sharp in the image, shutter speed is chosen to stop or show motion, as desired.  If those values are dependent variables (fixed for the shot, ISO becomes the independent variable.  In that case, there is no benefit to ISO 50, which was my point.  Of course, given the constraints of my personal range of acceptable ISO values (which is pretty broad on the 1D X!), I still cannot achieve the exposure I want, then I decide where to compromise.

But the key point is that ISO 50 offers no benefit, and can in some cases result in a detriment - therefore, I see no reason to use it.
Title: Re: ISO 50
Post by: agierke on January 21, 2013, 10:51:34 AM
i would like to now see Neoro and Mikael do a rendition of "Who's on First".
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 10:53:18 AM
Here is the dumbest question in the thread, but since I am the one that made the test, could I please ask what is HTP?

Not dumb at all. I've tried to expand the acronym at appropriate places, but obviously not everywhere it's appropriate.

HTP stands for Highlight Tone Priority. Rather than ISO 100 being the lowest selectable ISO, ISO 200 becomes the lowest selectable ISO. The camera actually exposes at ISO 100 but applies a tone curve to brighten the image. This has the end result of recording more highlight detail, but there's no such thing as a free lunch, so you get nosier shadows at the same time. If you're shooting raw, you can achieve the exact same result by shooting at ISO 100, underexposing by a stop, and brightening the image by a stop in post-production (with, of course, highlight compression to avoid digital clipping).

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 10:53:28 AM
Here is the dumbest question in the thread, but since I am the one that made the test, could I please ask what is HTP?

LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

Really, it's Highlight Tone Priority, which is a way to preserve one stop of highlights in an image (at the cost of an extra stop of noise in the shadows). 
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 10:56:44 AM
But the key point is that ISO 50 offers no benefit, and can in some cases result in a detriment - therefore, I see no reason to use it.

I, too, have no use for ISO 50 nor HTP. But I would find it useful if I were shooting JPEGs with no intention of post-processing, or if I were planning on doing ETTR or ETTL (respective) exposure and wanted a closer preview image on the back of the camera -- say, if a clueless client were looking over my shoulder.

Cheers,

b&
Title: Re: ISO 50
Post by: TheSuede on January 21, 2013, 11:12:18 AM
Regardless of camera brand I often recommend using 'HTP' or whatever acronym a particular brand has chosen to signify a more gentle contrast curve towards the clipped highlights when shooting outdoors in sunny weather. -But for jpg shooters only!.

Often there's something more involved in the altered process too, like a different color profile, local contrast enhancements and/or other 'optimizations' and so on. And I do dislike the often overly contrasty rendition that most in-camera jpg engines use. Using HTP in stead of just lowering the 'contrast' setting does in that case often have several benefits.
Title: Re: ISO 50
Post by: Marsu42 on January 21, 2013, 11:19:01 AM
Regardless of camera brand I often recommend using 'HTP' or whatever acronym a particular brand has chosen to signify a more gentle contrast curve towards the clipped highlights when shooting outdoors in sunny weather.

When I got my 60d I was shooting htp all the time in sunny weather, but stopped doing so because it increases the sensor's main weakness: high noise levels after raising shadows.

I admit clipped highlights are the worst thing that can happen, but it's closely followed by shadow noise - so today I only enable htp for jpeg and when I know the scene has a tendency to clip hightlights and I won't have to raise shadows in post a lot.
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 11:29:08 AM
Regardless of camera brand I often recommend using 'HTP' or whatever acronym a particular brand has chosen to signify a more gentle contrast curve towards the clipped highlights when shooting outdoors in sunny weather.

When I got my 60d I was shooting htp all the time in sunny weather, but stopped doing so because it increases the sensor's main weakness: high noise levels after raising shadows.

I admit clipped highlights are the worst thing that can happen, but it's closely followed by shadow noise - so today I only enable htp for jpeg and when I know the scene has a tendency to clip hightlights and I won't have to raise shadows in post a lot.

Me same
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 11:38:28 AM
Regardless of camera brand I often recommend using 'HTP' or whatever acronym a particular brand has chosen to signify a more gentle contrast curve towards the clipped highlights when shooting outdoors in sunny weather. -But for jpg shooters only!.

There's some slightly better and simpler advice you could offer JPEG shooters: do whatever you have to to make the image on the back of the camera look the way you want it to. Those on-camera knobs are the only ones you have to fiddle, so fiddle with them until you're happy with the result.

And HTP is an excellent in-camera implementation of "ETTL" (expose-to-the-left) post-processing, and perfect for situations where you care about highlights and won't see noise in shadows. Similarly, ISO 50 does a great job of doing exactly what ETTR does, when it's shadow noise you're worried about and don't care if the highlights blow. If you're shooting JPEG, you should know what each does and when to use either -- as well as when not to use them.

But, if you're shooting raw (and, generally, you should be if your post processing is much more than picking keepers), you should also understand what HTP and ISO 50 are doing, and why you're better off doing what they do yourself. Maybe it's an especially contrasty scene, and a single stop of ETTL isn't enough to keep those highlights you're so interested in, so you'll want to underexpose not by one stop but by two stops, for example.

Cheers,

b&
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 11:48:09 AM
Maybe it's an especially contrasty scene, and a single stop of ETTL isn't enough to keep those highlights you're so interested in, so you'll want to underexpose not by one stop but by two stops, for example.

I eagerly await Mikael's comment that in such a situation, one should instead use a D800 where the motive can be to underexpose by four stops and allow bringing up of shadows without motive of banding and noise.  I understand the technique works very well for sunrises, sunsets, cluttered sheds, and barbecues with QPcards on them.

EDIT: too late, Mikael beat me to the punch.  ???
Title: Re: ISO 50
Post by: Aglet on January 21, 2013, 01:22:10 PM
LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

 'Half The Photons' is correct IF you concede that enabling HTP raised the effective ISO amplification +1EV from whatever ISO you were at before activating HTP.
so the resultant metering of course causes a -1 EV exposure - and HALF THE PHOTONS! :)

Did you not understand what Michael meant vs what he may have typed or did you just feel the urge to have a battle from the same side of the argument?

Honestly, Neuro, we appreciate your extensive technical knowledge but some of us old guys are occasionally reminded of a a couple brothers scrapping over a toy by such an extensive display of (where do I get that cool little animation for) beating your head on a brick wall.

I hope you keep up your high rate of helpful and clear advice but temper it with a bit more restraint and human understanding in such cases.  I think you might have driven Michael to drinking after this thread. ;)
Title: Re: ISO 50
Post by: Meh on January 21, 2013, 02:03:45 PM
LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

 'Half The Photons' is correct IF you concede that enabling HTP raised the effective ISO amplification +1EV from whatever ISO you were at before activating HTP.
so the resultant metering of course causes a -1 EV exposure - and HALF THE PHOTONS! :)

Did you not understand what Michael meant vs what he may have typed or did you just feel the urge to have a battle from the same side of the argument?

Honestly, Neuro, we appreciate your extensive technical knowledge but some of us old guys are occasionally reminded of a a couple brothers scrapping over a toy by such an extensive display of (where do I get that cool little animation for) beating your head on a brick wall.

I hope you keep up your high rate of helpful and clear advice but temper it with a bit more restraint and human understanding in such cases.  I think you might have driven Michael to drinking after this thread. ;)

Why would any of us concede to your explanation when that is not what HTP does.  HTP does not change the aperture or shutter speed and therefore does not change the number of photons that are incident on the sensor.

We all understand what Mikael meant because he was very clear about it.  He was also very clear about his condescending remarks such as "look at the attached link, can't you boys read" when in fact the attached article exactly refuted his statements.
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 02:26:03 PM
LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

 'Half The Photons' is correct IF you concede that enabling HTP raised the effective ISO amplification +1EV from whatever ISO you were at before activating HTP.
so the resultant metering of course causes a -1 EV exposure - and HALF THE PHOTONS! :)

Sorry, but you seem to be falling into the same trap and suffering from the same misconceptions as Mikael.

It's only half the photons if the aperture is set a stop narrower or the shutter speed is set a stop faster. Are you suggesting that enabling HTP directly affects aperture or shutter speed? 

In fact, enabling HTP does nothing to the resultant metering - the camera meters for the ISO you select, it doesn't indicate that it's actually exposing at a 1-stop lower ISO, but it is (and that's why ISO 100 is unavailable with HTP enabled).  Try it - set ISO 200 or higher (but not a H expansion, since those are unavailable with HTP), meter a scene, then toggle HTP and see if the metering changes - does it?  Even in P Mode with Auto ISO where the camera is selecting all the parameters, enabling HTP does not change the aperture, shutter speed, or ISO selected. 

HTP doesn't raise the ISO, unless you have it set lower than ISO 200 before enabling HTP (and if you're at an H expansion ISO, enabling HTP lowers it).  I concede that in the specific case of the camera being set to ISO 100 before enabling HTP, the metered exposure will change by one stop, and IF you are in an auto exposure mode or you manually adjust exposure to compensate by one stop, then the number of photons will be halved.  Also 'halved' applies only if ISO 100 was set - if it was set to 50, 125, or 160, the change will be more or less than one stop (but not 'halved').  But that's a byproduct of how HTP works, applicable in a limited range of circumstances.  To conclude that reducing the photons by half is the mechanism by which HTP works is like concluding that a stopped analog clock is keeping correct time because you just happened to look at it at whatever time at which it was stuck.

As for misunderstanding Mikael, as I indicated earlier and Meh just wrote, that's clearly not the case.  He specifically stated, at least five times in at least four different posts, that HTP halves the number of photons and/or the amount of light hitting the sensor, and used that phrasing in describing the mechanism of HTP.  That manifestly demonstrates that his understanding of how HTP really works is seriously flawed, and if you are supporting that explanation, you are also failing to understand how HTP works.
Title: Re: ISO 50
Post by: ilkersen on January 21, 2013, 02:27:57 PM
Long thread, but clear and informative.  Thanks guys!

Take home message:  No need to use ISO50, ever ;)
Title: Re: ISO 50
Post by: TrumpetPower! on January 21, 2013, 02:39:46 PM
Long thread, but clear and informative.  Thanks guys!

Take home message:  No need to use ISO50, ever ;)

Almost.

For JPEG shooters, ISO 50 is the best way to do ETTR, for situations where you need the cleanest possible shadows and don't care about blown highlights. It's also useful for JPEG shooters who wished they had a one-stop neutral density filter but don't -- and, again, who can tolerate the loss of the last top of highlights.

Granted, the set of situations where either applies is so close as to be practically nonexistent...but there's at least the theoretical possibility it might apply somewhere sometime.

Cheers,

b&
Title: Re: ISO 50
Post by: Positron on January 21, 2013, 02:43:34 PM
My test.
1. It is unscientific, do not pounce on me. Am learning!
2. Stats: 1dx. 24-70 II. Manual focus, exposure, WB (tungston). f5.6 1/4 and 1/8.

Its all for us to see, but to my eyes:
1. The tint at ISO 50 is truer. (This is next to my desk and I can make a visual comparison)
2. The blown whites between the statue and lamp is blown more on 50 ISO.
3. 50 ISO shows marginal noise and sharpness improvement. (This could of course be just my eyes playing games.) Or is there a shake? I did use a sturdy tripod.

Do you think I should make another test? If yes, how should I improve? :)

Thank you.

Sanjay

Thanks for the test sanj.

Personally, the blown highlights on the flower pattern and above the statue are more distracting to me than any marginal gain in sharpness from using ISO 50 offsets. If you are in a situation where no data exists near the saturation point, then you have lots of latitude to boost contrast anyway, and at that point it looks to me like the only difference between straight ETTR and ISO 50 is whether you apply the tone curve yourself or let the camera do it for you.
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 04:10:42 PM
well you can put  the d800, d600  at -6 stops then  you are even safer regarding blowing highlights in all photographic situations, nothing you can do with your cameras-or?

Sure. We've covered the fact that the D800's sensor has better DR than any current Canon sensor, ad infinitum.  Nothing new here.

Still no admission that you are wrong with your repeated statements about HTP working by reducing the amount of light falling on the sensor, 'eh?  Not even after accusing me and others of an inability to admit being wrong, 'eh?  I can't say I'm surprised.  I can't even say I'm disappointed, because I expected no better...
Title: Re: ISO 50
Post by: Aglet on January 21, 2013, 04:54:13 PM
LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

 'Half The Photons' is correct IF you concede that enabling HTP raised the effective ISO amplification +1EV from whatever ISO you were at before activating HTP.
so the resultant metering of course causes a -1 EV exposure - and HALF THE PHOTONS! :)

Sorry, but you seem to be falling into the same trap and suffering from the same misconceptions as Mikael.

It's only half the photons if the aperture is set a stop narrower or the shutter speed is set a stop faster. Are you suggesting that enabling HTP directly affects aperture or shutter speed? 

In fact, enabling HTP does nothing to the resultant metering - the camera meters for the ISO you select, it doesn't indicate that it's actually exposing at a 1-stop lower ISO, but it is (and that's why ISO 100 is unavailable with HTP enabled).  Try it - set ISO 200 or higher (but not a H expansion, since those are unavailable with HTP), meter a scene, then toggle HTP and see if the metering changes - does it?  Even in P Mode with Auto ISO where the camera is selecting all the parameters, enabling HTP does not change the aperture, shutter speed, or ISO selected. 

HTP doesn't raise the ISO, unless you have it set lower than ISO 200 before enabling HTP (and if you're at an H expansion ISO, enabling HTP lowers it).  I concede that in the specific case of the camera being set to ISO 100 before enabling HTP, the metered exposure will change by one stop, and IF you are in an auto exposure mode or you manually adjust exposure to compensate by one stop, then the number of photons will be halved.  Also 'halved' applies only if ISO 100 was set - if it was set to 50, 125, or 160, the change will be more or less than one stop (but not 'halved').  But that's a byproduct of how HTP works, applicable in a limited range of circumstances.  To conclude that reducing the photons by half is the mechanism by which HTP works is like concluding that a stopped analog clock is keeping correct time because you just happened to look at it at whatever time at which it was stuck.

As for misunderstanding Mikael, as I indicated earlier and Meh just wrote, that's clearly not the case.  He specifically stated, at least five times in at least four different posts, that HTP halves the number of photons and/or the amount of light hitting the sensor, and used that phrasing in describing the mechanism of HTP.  That manifestly demonstrates that his understanding of how HTP really works is seriously flawed, and if you are supporting that explanation, you are also failing to understand how HTP works.

Actually, I think all we experienced types know how HTP works as many have amply explained it.
I think this very long argument is in the semantics of describing the comparison of HTP to non-HTP is where I see the confusion.

Now I'm trying to explain what I think Michael was trying to explain regarding HTP and losing half the photons and how this argument got started.
Like Suede, I read enough of this thread to see that all of you experienced tech guys DO understand HTP but I think your methods of explaining it are being misunderstood by some.  This is quite possibly a result of different linguistic syntax, typos, or lack of clear explanation by someone who should have been getting more sleep. ;D

Michael, correct me if I am wrong.
I think Michael WAS basing his explanation on the base of 100 ISO, and that enabling HTP now means you no longer have it available so your HTP base ISO is now 200 ISO and, therefore, you'll be using half the photons to create the same tone you would have if you were still using 100 ISO. 
I know you all understand this and you as well conceded this in this specific case in your 2nd last paragraph, above.
This is the foundation of how HTP works. Agreed, yes?
Because, regardless of this argument, we all know that one full step up in ISO means we'll now be using half the photons to create a given tone or shade.

I think this got out of context when thinking about the higher ISO settings, with and w-o HTP

E.G. If we take a normal 800 ISO setting and require 100 photons per pixel to generate some shade.
at 1600 ISO we should only require 50 photons to generate the same shade or 200 photons at 400 ISO.

we're still good to this point too, yes?

now we turn on HTP and set to ISO 800
The metering is the same as for the normal ISO 800, hence the exposure is the same and we still use 100 photons to create the same shade.

But behind the scenes, inside the camera, the ISO (sensor gain) is actually ISO 400, and the subsequent processing of this raw file is tweaked so that those 100 photons create the same shade as they did with non-HTP 800 ISO.
The HTP advantage is that since the shot was really done, internal to the camera, at a 400 ISO sensitivity there's 1EV more headroom in the highlights available and the processing allows for a more gradual transfer curve near the top EV levels to prevent or reduce the likelihood of clipping bright shades of gray-white.
The HTP disadvantage is that this comes at the expense of signal to noise ratio which is most evident in shadow areas where fixed read noise becomes a considerable amount relative to the small signal of darker tones/shades.

we're still good ?..  I know what I'm talking about?.. :)

I think Michael merely views an HTP ISO 800 as ISO 400, 1600HTP as 800, etc.
I think his viewpoint is from INSIDE the sensor, and this does not surprise me considering how attentive he is to sensor metrics.
If you view things in this way then you ARE using half the photons compared to using the normal ISO and exposing appropriately.
If you view things in this way then you ARE changing the metering and therefore the exposure and the number of photons/electrons by -1 stop.
When using HTP you ARE getting more shadow noise for a given shade because it's only using half the photons to create compared to using the one step lower non-HTP ISO.

I think perhaps Michael did not succeed in making his point of view clearly to those of us who look at this from a different viewpoint is all.
If I had to explain this in another language i don't think i'd do a very good job of it myself.

I hope I presented a clear explanation of what I think is Michael's viewpoint.

Did I help clear anything up for anybody?
Title: Re: ISO 50
Post by: jpthurston on January 21, 2013, 04:54:55 PM
I know there are a multitude of factors affecting the process in shooting in the 5D Mark III's expanded ISO 50;SNR, DR, electronics, physics, optics, post work in software, brand model specifications and hype, third party testing...on and on.
Many of those topics can be throughly argued far beyond my understanding of technical issues at hand, but actually prove nothing but a great debate topic amongst experts.

I think the real test of whether shooting @ ISO 50 with the 5D MKIII is usable or not is to actually go out and to test it yourself, not endlessly beat it to death without a single exposure to evaluate.

Admittedly this was shot on an overcast day without glaring highlights, and I really wanted to accentuate the waterfall's movement, so I used a Circ. Polarizer not for reflections control, but to add 2+ stops exposure in addition to lowering the ISO to 50. I don't yet have a decent ND filter set to accomplish the same thing.

I was please enough with the results shot at Mission Trails Park Old Padre Dam, built around 1800 and of the first Spanish irrigation structures in California on the San Diego River. No it is not Old Man river, but yes we have a flowing river here!

Certainly open to opinions and criticism. Specs: 5D MKIII 17-40 f4, ISO 50, @ 5 sec , @f18
Title: Re: ISO 50
Post by: neuroanatomist on January 21, 2013, 05:34:09 PM
Did I help clear anything up for anybody?

Nice try, but no.  If you choose to believe that Mikael understands clearly and is simply communicating that in a way we aren't comprehending, you're certainly welcome to your belief.  I see no evidence of that, quite the opposite...I see intransigent repetition of the same incorrect statements, but the statements themselves are articulated clearly.  Even if your assumption is correct, I'd say that someone who chooses a specific case that is an exception to the norm to describe a process (and hammers that same point over and over) has at best a limited grasp of the concepts behind that process. 
Title: Re: ISO 50
Post by: rpt on January 21, 2013, 09:49:50 PM
I know there are a multitude of factors affecting the process in shooting in the 5D Mark III's expanded ISO 50;SNR, DR, electronics, physics, optics, post work in software, brand model specifications and hype, third party testing...on and on.
Many of those topics can be throughly argued far beyond my understanding of technical issues at hand, but actually prove nothing but a great debate topic amongst experts.

I think the real test of whether shooting @ ISO 50 with the 5D MKIII is usable or not is to actually go out and to test it yourself, not endlessly beat it to death without a single exposure to evaluate.

Admittedly this was shot on an overcast day without glaring highlights, and I really wanted to accentuate the waterfall's movement, so I used a Circ. Polarizer not for reflections control, but to add 2+ stops exposure in addition to lowering the ISO to 50. I don't yet have a decent ND filter set to accomplish the same thing.

I was please enough with the results shot at Mission Trails Park Old Padre Dam, built around 1800 and of the first Spanish irrigation structures in California on the San Diego River. No it is not Old Man river, but yes we have a flowing river here!

Certainly open to opinions and criticism. Specs: 5D MKIII 17-40 f4, ISO 50, @ 5 sec , @f18
Nice picture. I like the brick wall and the flow of the water.

I have a few questions:
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 10:32:22 PM
Could I explore and investigate this a bit further?
We, or rather I, by now feel:
a) I was mistaken about noise advantage of ISO 50.
b) ISO 50 causes loss of highlights.
c) I will not use ISO 50 again.

I examined the histograms of the two shots I posted earlier as test.
Although I exposed both shots equally, (And I cant be convinced otherwise) but the histogram on the 50 ASA shows that whites are clipping.... What does this mean? To my non technical mind it says: At ISO 50 the dynamic range gets reduced. Am I wrong?

I am not agree or disagreeing with many posts here, just exploring. Actually I do not even understand many posts fully to argue! :)
Title: Re: ISO 50
Post by: sanj on January 21, 2013, 11:50:26 PM
I used ISO 50 a lot in my 5Dc because of how super smooth the files looked. The 5d3, not so much.

I feel the same.
Title: Re: ISO 50
Post by: jpthurston on January 21, 2013, 11:51:24 PM
I know there are a multitude of factors affecting the process in shooting in the 5D Mark III's expanded ISO 50;SNR, DR, electronics, physics, optics, post work in software, brand model specifications and hype, third party testing...on and on.
Many of those topics can be throughly argued far beyond my understanding of technical issues at hand, but actually prove nothing but a great debate topic amongst experts.

I think the real test of whether shooting @ ISO 50 with the 5D MKIII is usable or not is to actually go out and to test it yourself, not endlessly beat it to death without a single exposure to evaluate.

Admittedly this was shot on an overcast day without glaring highlights, and I really wanted to accentuate the waterfall's movement, so I used a Circ. Polarizer not for reflections control, but to add 2+ stops exposure in addition to lowering the ISO to 50. I don't yet have a decent ND filter set to accomplish the same thing.

I was please enough with the results shot at Mission Trails Park Old Padre Dam, built around 1800 and of the first Spanish irrigation structures in California on the San Diego River. No it is not Old Man river, but yes we have a flowing river here!

Certainly open to opinions and criticism. Specs: 5D MKIII 17-40 f4, ISO 50, @ 5 sec , @f18
Nice picture. I like the brick wall and the flow of the water.

I have a few questions:
  • Did you shoot raw or JPEG?
  • Your file name has the word "edit" in it. What editing did you do?

I always shoot Full sized Raw for Landscapes @ 14 bit, Initially catalogue and process in 16-bit Adobe ProPhoto in Lightroom 4.3 using Process version 2012/ACR7, which in and off itself offers superior Highlight Recovery at any ISO. Image then is transferred to CS5 for further tonal edits, touchups, etc., and when it returns to Lightroom, it appends the filename with -edit.xxx. I export that to a JPEG for posting.
This is a real world workflow for producing printable imagery, not mind numbing photon counts in test images.

Pixel peepers might claim that the Lightroom and Photoshop edits obscures the Highlight clipping problems of  shooting @ ISO 50. Perhaps so, but I dont know of a real world digital workflow that doesn't include noise reduction, sharpening, and highlight/shadow clipping control to produce not only a workable and viewable, but printable image.
Does anybody print unprocessed RAW images out of the camera?

In the end isn't it all about getting the final product looking the the way you want it to appear?
A photographer let alone a lay viewer of a print is never going to say "Oh my God this image has 1/2 stop too little DR, he used HTP",  or "the sensor collected X Photons"
If one of my images had serious blown out highlights or shadow noise, and is therefore unacceptable, I simply wouldn't exhibit it.
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 01:32:02 AM
I know there are a multitude of factors affecting the process in shooting in the 5D Mark III's expanded ISO 50;SNR, DR, electronics, physics, optics, post work in software, brand model specifications and hype, third party testing...on and on.
Many of those topics can be throughly argued far beyond my understanding of technical issues at hand, but actually prove nothing but a great debate topic amongst experts.

I think the real test of whether shooting @ ISO 50 with the 5D MKIII is usable or not is to actually go out and to test it yourself, not endlessly beat it to death without a single exposure to evaluate.

Admittedly this was shot on an overcast day without glaring highlights, and I really wanted to accentuate the waterfall's movement, so I used a Circ. Polarizer not for reflections control, but to add 2+ stops exposure in addition to lowering the ISO to 50. I don't yet have a decent ND filter set to accomplish the same thing.

I was please enough with the results shot at Mission Trails Park Old Padre Dam, built around 1800 and of the first Spanish irrigation structures in California on the San Diego River. No it is not Old Man river, but yes we have a flowing river here!

Certainly open to opinions and criticism. Specs: 5D MKIII 17-40 f4, ISO 50, @ 5 sec , @f18
Nice picture. I like the brick wall and the flow of the water.

I have a few questions:
  • Did you shoot raw or JPEG?
  • Your file name has the word "edit" in it. What editing did you do?

I always shoot Full sized Raw for Landscapes @ 14 bit, Initially catalogue and process in 16-bit Adobe ProPhoto in Lightroom 4.3 using Process version 2012/ACR7, which in and off itself offers superior Highlight Recovery at any ISO. Image then is transferred to CS5 for further tonal edits, touchups, etc., and when it returns to Lightroom, it appends the filename with -edit.xxx. I export that to a JPEG for posting.
This is a real world workflow for producing printable imagery, not mind numbing photon counts in test images.

Pixel peepers might claim that the Lightroom and Photoshop edits obscures the Highlight clipping problems of  shooting @ ISO 50. Perhaps so, but I dont know of a real world digital workflow that doesn't include noise reduction, sharpening, and highlight/shadow clipping control to produce not only a workable and viewable, but printable image.
Does anybody print unprocessed RAW images out of the camera?

In the end isn't it all about getting the final product looking the the way you want it to appear?
A photographer let alone a lay viewer of a print is never going to say "Oh my God this image has 1/2 stop too little DR, he used HTP",  or "the sensor collected X Photons"
If one of my images had serious blown out highlights or shadow noise, and is therefore unacceptable, I simply wouldn't exhibit it.
Thanks. I am still learning the fine art of digital editing and so I am curious. I have LR 4.3 but not PS... As for pixel peeping or counting photons (or counting Half The Photons) I don't really care for that personally. To each their own...
Title: Re: ISO 50
Post by: sanj on January 22, 2013, 06:51:15 AM
@Neuro:
Neuro:
[/quote]
It's only half the photons if the aperture is set a stop narrower or the shutter speed is set a stop faster.
[/quote]

And not if ISO is reduced by a stop? Does the sensor not reject half the photons when it is 'asked' to be less sensitive?

Dont pounce on me, am learning here...

I can easily see that the amount of light reaching the sensor is a function of shutter/aperture combination. But am confused after that. I thought sensor reacts to the available light based on what ISO is set.
Thx...
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 07:24:33 AM
@Neuro:
Neuro:
Quote
It's only half the photons if the aperture is set a stop narrower or the shutter speed is set a stop faster.

And not if ISO is reduced by a stop? Does the sensor not reject half the photons when it is 'asked' to be less sensitive?

Dont pounce on me, am learning here...

I can easily see that the amount of light reaching the sensor is a function of shutter/aperture combination. But am confused after that. I thought sensor reacts to the available light based on what ISO is set.
Thx...
The ISO set determines the analog gain applied to the signal that resulted after photons are captured in the photo-site.
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 08:05:50 AM
And not if ISO is reduced by a stop? Does the sensor not reject half the photons when it is 'asked' to be less sensitive?

Dont pounce on me, am learning here...

I can easily see that the amount of light reaching the sensor is a function of shutter/aperture combination. But am confused after that. I thought sensor reacts to the available light based on what ISO is set.
Thx...

No one should be pounced on for trying to learn!

The sensor has no control over the number of photons it collects.  The maximum capacity is determined by the design of the sensor.  Only aperture and shutter open time determine the amount of photons collected during the exposure (up to the max capacity of a photosite, which is when highlight clipping becomes unavoidable).  After an exposure, each photosite is 'read out' and at that point, analog gain (amplification) is applied to the signal according to the ISO set.  In other words, every exposure has the photons being collected at "base ISO" (which is different for different for different sensor designs, but is usually somewhere in the 60 to 200 range).  Following that capture of photons, and conversion to do electrons by the photo site, the signal has been applied (positive or negative, (within the "native" range of ISOs), then the analog signal is converted to a digital signal, and if necessary based on the selected ISO, additional digital gain is applied (for the "expanded" ISOs).
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 09:19:28 AM
Neuro wrote: Sorry, but you seem to be falling into the same trap and suffering from the same misconceptions as Mikael.

No it is about words, and what we mean.

And where  is  my earlier  post?

HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room. ( I describe this as under exposure) because the camera  metering after 200iso)
You get the same effect by under exposing 100iso 1 stop  and later correct the raw file  in the raw converter
In Jpg the camera lay a smoother contrast curve which make a smoother high light reproduction and also lift little bit in lower levels which make the noise little bit visible.
I hope I have make this message readable
Have a nice day

pardon my intrusion here Mikael, but the words and concepts you are using in the above is not under question.  WHat is under question is the posts where you say that the HTP causes half the number of photons to reach the sensor. 
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 09:27:11 AM
Neuro wrote: Sorry, but you seem to be falling into the same trap and suffering from the same misconceptions as Mikael.

No it is about words, and what we mean.

And where  is  my earlier  post?

HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room. ( I describe this as under exposure) because the camera  metering after 200iso)
You get the same effect by under exposing 100iso 1 stop  and later correct the raw file  in the raw converter
In Jpg the camera lay a smoother contrast curve which make a smoother high light reproduction and also lift little bit in lower levels which make the noise little bit visible.
I hope I have make this message readable
Have a nice day

pardon my intrusion here Mikael, but the words and concepts you are using in the above is not under question.  WHat is under question is the posts where you say that the HTP causes half the number of photons to reach the sensor.
Yes Mikael, from my perspective you need to review you post on the first page where you mention this. You then say that results in half the charged electrons. That is not right. The same number of photons would be collected in the photo site irrespective if you has set HTP or not.

I hope you understand this. Afterwords, after all the photons are collected and a signal is generated, things happen resulting in what you describe in that post as "half the charged electrons"...

If you disagree with what I have written, do let me know what you disagree with.

Thanks.
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 09:35:29 AM
And where  is  my earlier  post?

The one where you made a derogatory remark directed at me?  No doubt it was deleted by a mod.

No it is about words, and what we mean.

HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room.   ( I describe this as  an under exposure) because the camera  is metering after 200iso)
You get the same effect by under exposing 100iso 1 stop  and later correct the raw file  in the raw converter
In Jpg the camera lay a smoother contrast curve which make a smoother high light reproduction and also lift little bit in lower levels which make the noise little bit more visible.
I hope I have make this message readable so every one can understand

Yes, that's essentially (or maybe exactly) what you've posted previously, and it's clear that you understand the consequences of enabling HTP. 

But it is about words, and many times you used words describing a 'halving of light', 'shorter exposure', and 'the sensor collects less photons' as part of the HTP process, all of which are false.  When that was brought to your attention, you simply restated the same incorrect information.  So while you certainly understand the results of HTP, it's not at all clear that you understand the underlying mechanism, which has nothing to do with altering the amount of light hitting the sensor.  Looking at the responses above, it's evident that I'm not the only one who is aware that you made incorrect statements about the underlying mechanism by which HTP works (i.e., it does not change exposure per se, but only the gain applied).

Regardless, it's clear that you have not acknowledged that you provided wrong information about that mechanism, and I suspect you're unlikely to do so.  That's rather ironic, given that you earlier accused others of being unable to admit their mistakes.  But as I previously stated, I'm not at all surprised by that...
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 10:04:16 AM
Mikael here is the confusion

1.  Your latest post is correct, i.e.
Quote
HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room

2.  But  the words you have used previously are quite clear, and quite incorrect,  namely about the amount of light hitting the sensor during HTP operation.   

mechanism behind HTP In a contrasty sunny day and at base iso  100iso there are no head room and the proximity to clippning is small.
By HTP there will be a under exposure to gain 1 stop of high lights. This is the same as  let the sensor be hit by the less amount of photons as compared to 100iso and numbers of created electrons just before readout are therefore less.
and there are now 1 stop  more of head room up to clipping.
The sensor collect photons  nothing else  and some of them will be in to electrons, there are also some gain going on.
To get the effect , lesser photons/less electrons and  to get 1 stop of high light head room the signal must be lower than it is at 100iso , this can be done by shorter exposure  time, change f-stop, earlier read out. + effect head room   - effect more noise in lower levels.
There is no way at 100iso when the sensels are  fully charged/near to clipping  can  get a negative amplification and  therby get 1 stop head room .
Since we call 100 iso (near fully charged cell) 100iso  and 200 iso 200 iso , the electron charge  has been halved  at 200iso and the gain has increased.
In HTP  the sensor  has now been hit by  less light/photons = that we called  1 stop under exposure and fewer electrons has been read out  which later  are adjusted in the raw converter by gain and different curve
This is the same as underexpose 100 iso 1 stop= 1 stop  faster shutter speed or 1 more F-stop to get 1 stop more head room  and then adjust the raw file and make a own smother curve at the top.

It would be most helpful if you would rationalize the statements you have made that appear to conflict with each other.  If your understanding has progressed, and you no longer believe that HTP causes a change in the number of photons hitting the sensor, then please say that.   Instead, your English is really quite good and to me you are trying to write as an authority, which invites us to put your statements side by side.
Title: Re: ISO 50
Post by: Marsu42 on January 22, 2013, 10:21:53 AM
And where  is  my earlier  post?
The one where you made a derogatory remark directed at me?  No doubt it was deleted by a mod.
But it was just getting entertaining, I really liked neuro's "Can you not be insulting, boy?" post :->

So while you certainly understand the results of HTP, it's not at all clear that you understand the underlying mechanism, which has nothing to do with altering the amount of light hitting the sensor.
Ok, to be on topic: I doubt Canon is very keen on people knowing what htp actually does because it sounds like "fix limited sensor dr at no cost": the latest manual on the 6d simply says on p.92: "You can minimize overexposed highlight areas" and that's certainly a good thing, isn't it?

I remember because when I asked what htp is good for I first got flamed for not simply reading the manual, people obviously don't even realize there is something to ask about concerning iso50/htp... http://www.canonrumors.com/forum/index.php?topic=5687.msg108754#msg108754 (http://www.canonrumors.com/forum/index.php?topic=5687.msg108754#msg108754)
Title: Re: ISO 50
Post by: TheSuede on January 22, 2013, 11:25:16 AM
Mikael here is the confusion

1.  Your latest post is correct, i.e.
Quote
HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room

2.  But  the words you have used previously are quite clear, and quite incorrect,  namely about the amount of light hitting the sensor during HTP operation.   

mechanism behind HTP In a contrasty sunny day and at base iso  100iso there are no head room and the proximity to clippning is small.
By HTP there will be a under exposure to gain 1 stop of high lights. This is the same as  let the sensor be hit by the less amount of photons as compared to 100iso and numbers of created electrons just before readout are therefore less.
and there are now 1 stop  more of head room up to clipping.
The sensor collect photons  nothing else  and some of them will be in to electrons, there are also some gain going on.
To get the effect , lesser photons/less electrons and  to get 1 stop of high light head room the signal must be lower than it is at 100iso , this can be done by shorter exposure  time, change f-stop, earlier read out. + effect head room   - effect more noise in lower levels.
There is no way at 100iso when the sensels are  fully charged/near to clipping  can  get a negative amplification and  therby get 1 stop head room .
Since we call 100 iso (near fully charged cell) 100iso  and 200 iso 200 iso , the electron charge  has been halved  at 200iso and the gain has increased.
In HTP  the sensor  has now been hit by  less light/photons = that we called  1 stop under exposure and fewer electrons has been read out  which later  are adjusted in the raw converter by gain and different curve
This is the same as underexpose 100 iso 1 stop= 1 stop  faster shutter speed or 1 more F-stop to get 1 stop more head room  and then adjust the raw file and make a own smother curve at the top.

It would be most helpful if you would rationalize the statements you have made that appear to conflict with each other.  If your understanding has progressed, and you no longer believe that HTP causes a change in the number of photons hitting the sensor, then please say that.   Instead, your English is really quite good and to me you are trying to write as an authority, which invites us to put your statements side by side.

Now does those quote chains get long, damn... :)
Mikael should handle his own words, but in the text you quote in the second part, the words "ISO" and "100" are sprinkled all over the place. I think the main bulk of the confusion lies here. At ISO100, the exposure that's normally set by the camera in "automatic" mode approaches the physical charge storage limit of the sensor. Hence, the ISO50 fake setting is close to useless in reality for anyone that shoots raw (but not for people that shoot jpg - Canon's jpg-in-camera contrast curve does normally leave quite a lot of image material close to blown white out of the jpg - so there's still room to nudge the image brightness a bit more in post before saving the jpg)

What happens at higher ISOs (than 100) and with HTP is another story.
Since the actual aperture and shutter speed does not change when activating HTP, photometric exposure stays constant - i.e no loss of photons, and also hence no increase in natural Poisson noise. The only loss you get is that you boost the relative levels of electronic noise and read noise per gray level by one stop by first halving conversion ratio and then boosting that in software.
When you halve conversion ratio (ISO) the electronic noise and RN still stays the same
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 11:34:45 AM
good point -- as  neuro suggested its the special case that got promoted to the general case thats confusing.  you're right lets let Mikael explain what he really means by "the mechanism of HTP", halving of photons, and "HTP is nothing more than ..."  right now, whether due to a lanuage problem, not understanding the difference between an electron and a photon, differences in the behavior of HTP at ISO 100 versus 200 whatever... the explanations are a curious mixure of truth and error without a clear delineation of which is which. 
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 11:37:26 AM
(Snip!)

What happens at higher ISOs (than 100) and with HTP is another story.
Since the actual aperture and shutter speed does not change when activating HTP, photometric exposure stays constant - i.e no loss of photons...

(Snip!)
Dang! Silly me, I thought Mikael had found a way to set his Canon camera to HTP and control how the Sun streamed Photons towards his sensor!

You just burst my bubble.
 :(
Title: Re: ISO 50
Post by: RLPhoto on January 22, 2013, 11:39:33 AM
This thread just shows how much of us could really use a "True" ISO 50 in DSLR's. I'd like one canon and perhaps they will be the first with the new 1Dxs.
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 11:42:09 AM
This thread just shows how much of us could really use a "True" ISO 50 in DSLR's. I'd like one canon and perhaps they will be the first with the new 1Dxs.

+1 to that.  perhaps the new crop of sensors may have that capability to appear on the big MP body that exists only in the imagination right now :D
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 11:50:06 AM
This thread just shows how much of us could really use a "True" ISO 50 in DSLR's. I'd like one canon and perhaps they will be the first with the new 1Dxs.

The problem is that there's no free lunch.  A "true" ISO 50 would mean a lower base ISO, meaning that to achieve higher ISOs, even more amplification would be needed - meaning more high ISO noise.  Usually, if ISO 100 is not low enough, one stop more is insufficient, at least in terms of shutter speed.  The waterfall example posted earlier at ISO 50 and 5 s exposure required f/18 to get there - personally, I'd have preferred to shoot that at f/9 and ISO 100 with a 3-stop ND.
Title: Re: ISO 50
Post by: RLPhoto on January 22, 2013, 11:53:36 AM
This thread just shows how much of us could really use a "True" ISO 50 in DSLR's. I'd like one canon and perhaps they will be the first with the new 1Dxs.

The problem is that there's no free lunch.  A "true" ISO 50 would mean a lower base ISO, meaning that to achieve higher ISOs, even more amplification would be needed - meaning more high ISO noise.  Usually, if ISO 100 is not low enough, one stop more is insufficient, at least in terms of shutter speed.  The waterfall example posted earlier at ISO 50 and 5 s exposure required f/18 to get there - personally, I'd have preferred to shoot that at f/9 and ISO 100 with a 3-stop ND.

The 1Dxs would be a 46mp+, pure studio camera from practical use from 50-800 ISO. IE: the S designation.

It would return back to its true roots as a studio camera.
Title: Re: ISO 50
Post by: R1-7D on January 22, 2013, 11:54:41 AM
Neuro, I initially joined this Forum because of you. Your knowledge on all this camera equipment blows my mind. This thread is another great educational experience.


Title: Re: ISO 50
Post by: rpt on January 22, 2013, 12:04:18 PM
This thread just shows how much of us could really use a "True" ISO 50 in DSLR's. I'd like one canon and perhaps they will be the first with the new 1Dxs.

The problem is that there's no free lunch.  A "true" ISO 50 would mean a lower base ISO, meaning that to achieve higher ISOs, even more amplification would be needed - meaning more high ISO noise.  Usually, if ISO 100 is not low enough, one stop more is insufficient, at least in terms of shutter speed.  The waterfall example posted earlier at ISO 50 and 5 s exposure required f/18 to get there - personally, I'd have preferred to shoot that at f/9 and ISO 100 with a 3-stop ND.
My two cents (and I am not disclosing the currency) is that to get a "true" ISO 100 if we need 14 bits, for a "true" ISO 50 we will need 15 bits. I am willing to bet that if you wait a bit longer, we will get native ISO 25 (how did I figure that? Well, 16 bits...). Now Einstein said time is relative so I guess the "bit" he was talking about was not a 0 or a 1...

Title: Re: ISO 50
Post by: Aglet on January 22, 2013, 12:35:37 PM
Mikael here is the confusion

1.  Your latest post is correct, i.e.
Quote
HTP is nothing else than while the camera metering for 200iso  the gain is smaller (around 100iso gain) and thereby we get a head room

2.  But  the words you have used previously are quite clear, and quite incorrect,  namely about the amount of light hitting the sensor during HTP operation.   

mechanism behind HTP In a contrasty sunny day and at base iso  100iso there are no head room and the proximity to clippning is small.
By HTP there will be a under exposure to gain 1 stop of high lights. This is the same as  let the sensor be hit by the less amount of photons as compared to 100iso and numbers of created electrons just before readout are therefore less.
and there are now 1 stop  more of head room up to clipping.
The sensor collect photons  nothing else  and some of them will be in to electrons, there are also some gain going on.
To get the effect , lesser photons/less electrons and  to get 1 stop of high light head room the signal must be lower than it is at 100iso , this can be done by shorter exposure  time, change f-stop, earlier read out. + effect head room   - effect more noise in lower levels.
There is no way at 100iso when the sensels are  fully charged/near to clipping  can  get a negative amplification and  therby get 1 stop head room .
Since we call 100 iso (near fully charged cell) 100iso  and 200 iso 200 iso , the electron charge  has been halved  at 200iso and the gain has increased.
In HTP  the sensor  has now been hit by  less light/photons = that we called  1 stop under exposure and fewer electrons has been read out  which later  are adjusted in the raw converter by gain and different curve
This is the same as underexpose 100 iso 1 stop= 1 stop  faster shutter speed or 1 more F-stop to get 1 stop more head room  and then adjust the raw file and make a own smother curve at the top.

It would be most helpful if you would rationalize the statements you have made that appear to conflict with each other.  If your understanding has progressed, and you no longer believe that HTP causes a change in the number of photons hitting the sensor, then please say that.   Instead, your English is really quite good and to me you are trying to write as an authority, which invites us to put your statements side by side.

Maybe it's all the foreign language manuals, schematics and engineers in person that I have to decipher..
.. because despite the imperfect english grammar and syntax, I understood perfectly well what Michael stated in that quote above.
Now it's important to many of us with tech-geek credentials to use the most correct terminology possible to describe something properly, lest we be misunderstood.. or worse.  I'm willing to cut people plenty of linguistic slack as they try to describe something in a language as convoluted as english, whether it's their first language or not.

ISO 50 = YES, wish i had it available as a real ISO at times.

BTW, as an extra, i shots some crude tests with my UN-beloved 5D2 last night.
MIDTONE BANDING at iso 100 - it still has it!
  Real-world photos are where I first found the problem, specific test shots certainly replicate it.  I need to do a few more tests just to make sure this is not a glitch of my display calibration curve but I'm pretty sure it isn't as I can accentuate the pattern with a simple unsharp function in PS.
Should i start a new topic with that when I get a chance?
Title: Re: ISO 50
Post by: Marsu42 on January 22, 2013, 12:42:32 PM
BTW, as an extra, i shots some crude tests with my UN-beloved 5D2 last night.
MIDTONE BANDING at iso 100 - it still has it!
  Real-world photos are where I first found the problem, specific test shots certainly replicate it.  I need to do a few more tests just to make sure this is not a glitch of my display calibration curve but I'm pretty sure it isn't as I can accentuate the pattern with a simple unsharp function in PS.
Should i start a new topic with that when I get a chance?

Sure - bashing the 5d2 will make the 6d look better, and I'm desperate for that since this is most probably the ff camera I can/want to afford over the 5d3 :-p
Title: Re: ISO 50
Post by: J.R. on January 22, 2013, 01:13:43 PM

Should i start a new topic with that when I get a chance?

Yes please ... I'm interested in this

Cheers ... J.R.
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 01:35:48 PM
Maybe it's all the foreign language
In my universe, Physics and Mathematics speak one language.

Btw, I have asked questions and have not got one response. Well, may be I am dark matter... ::)
Title: Re: ISO 50
Post by: RLPhoto on January 22, 2013, 01:44:20 PM

BTW, as an extra, i shots some crude tests with my UN-beloved 5D2 last night.
MIDTONE BANDING at iso 100 - it still has it!
  Real-world photos are where I first found the problem, specific test shots certainly replicate it.  I need to do a few more tests just to make sure this is not a glitch of my display calibration curve but I'm pretty sure it isn't as I can accentuate the pattern with a simple unsharp function in PS.
Should i start a new topic with that when I get a chance?

You keep saying this but are always unable to post a photo illustrating it, whenever you are asked for one, or the percentage of your images you loose to it, you leave the thread.

Can we see some of these real world images that you consider unusable?

Indeed, I'd like to see those as well.
Title: Re: ISO 50
Post by: TheSuede on January 22, 2013, 01:52:58 PM

The problem is that there's no free lunch.  A "true" ISO 50 would mean a lower base ISO, meaning that to achieve higher ISOs, even more amplification would be needed - meaning more high ISO noise.  Usually, if ISO 100 is not low enough, one stop more is insufficient, at least in terms of shutter speed.  The waterfall example posted earlier at ISO 50 and 5 s exposure required f/18 to get there - personally, I'd have preferred to shoot that at f/9 and ISO 100 with a 3-stop ND.

-And that's why you need low RN and PRNU. I wonder why that very, very practical connection is so hard to understand.
The almost two-stop DR advantage you get at base ISO with very low-noise electronics and sensors give basically the same effect on images in real-world use as having a true ISO50 in a camera with more electronic noise.

When object-related noise (Poisson) is low enough to be well below the visibility threshold, there's very little more to be gained by lowering the base ISO. The only area in the image where there would be a true practical - visible - advantage to have more photometric exposure on the sensor is in the deep shadows, to lift the capture noise level above the electronic noise, that is the dominant factor in the shadows at low ISOs in Canon cameras.

What Mikael is usually on about is the undeniable fact that many Sony sensors have an electronic noise level that enables you to shoot at close to -2Ev from normal exposure at base ISO with virtually no detrimental effect in the resulting image - compared to a Canon camera at normal +/-0Ev exposure. At normal daylight levels of light, you can shoot the D800 at 1/800s F8.0 ISO100, and the shadows will still be cleaner and contain more real color and detail than any canon camera shot at twice the exposure - i.e like 1/400s F8.0 ISO100.

Add a 1 or 2-stop ND on top of that, and you have a virtual ISO50 or ISO25 camera with extremely small hidden penalties, bordering on undetectable compared to a "true" ISO50 or ISO25 image on visual inspection.

(sorry, just had to state some obvious facts that many here tend to want to pass by unnoticed...) :)
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 02:01:13 PM
@TheSuede, agreed - and may I add, I'd love to see such performance (very low read noise at base ISO) from a Canon sensor!
Title: Re: ISO 50
Post by: Don Haines on January 22, 2013, 02:43:01 PM
I've never been that worried about low ISO.... just slap on a ND8 filter, set to ISO200, and pretend I'm shooting Kodachrome 25....

I'm not a camera sensor expert, but I do know electronics.... As a general rule the extreme ends of a sensor's range are non-linear and more prone to noise. I would not be supprised to hear that ISO200 has less noise than ISO100. Ideally, what we want to do is to shift our light levels to the more linear range of the sensor. If it too bright, the ND filter comes to our rescue.... if it is too dark we wait for a better sensor.
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 04:51:53 PM
pardon my intrusion here Mikael, but the words and concepts you are using in the above is not under question.  WHat is under question is the posts where you say that the HTP causes half the number of photons to reach the sensor.

Not at all.
what I meant was that (and I hope I use the right words now so you all can understand me) that the camera is metering at 200iso and  also exposed after 200 iso ,  1 stop less/shorter than base iso  100 = shorter time or 1 more f-stop..
At 200 iso there are already created" a head room," se my picture,it is old and used many times,   the sensor charge/electrons i now halved compare to 100iso .And for every iso stop there are a halving (se the picture)
In a regular 200iso exposure this head rooms  are then  analog gained "200iso"
In HTP the gain is "100 iso"  and  to created a headroom for adjustments and  another smoother  curve.
The same thing as under expose 100iso one stop and then adjust the raw file with own curve etc in the raw converter.
[/quote]

ok, but I have to ask the obvious question: you are offering this as a general explanation of how HTP works at all times?    when someone asks what happens to their camera when they turn HTP on, you going to tell them that half the photos reach the sensor without asking them where they have already set the ISO dial? 
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 05:07:20 PM
and if they have the ISO set already to 200 or 400 or 800 or 160 or 1600, or a great many other values other than 100,  and they turn on HTP,  what will you will tell them?  what will you tell the vast majority of photographers in the vast majority of the camera settings they already use most of the time.  how will you explain the HTP mechanism to them?
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 05:59:47 PM
That they gain a head room and a better reproduction of the high lights if they shoot JPG  and don't know raw, under or over  exposure, post processing etc .

no -- that is not the mechanism that is the  benefit.  how will you explain the HTP mechanism, the effect of exposure, and the number of photons striking the sensor.
Title: Re: ISO 50
Post by: TheSuede on January 22, 2013, 06:52:56 PM
Yes, compared to using the camera at ISO100, turning HTP on makes the camera expose for at least ISO200, which is a full stop difference in photometric exposure. A halving of the number of photons captured in a normal case camera-choice automatic exposure. True. But that's the intention and planned execution of the function, so that particular point needs no further discussion in my view.

You could negate this by setting the camera at ISO100, turn HTP on and then add +1Ev exposure compensation at the same time, but then the camera would probably commit suicide from pure confusion.
At this point you're trading insults more than you're trading information - hardly a constructive scenario.

Shooting raw, there can never be more headroom in any possible and imaginable scenario than when shooting at ISO100 and exposing correctly for the scene. This means underexposure compared to the in-camera automatic measurement if the scene contains highlights in which you want to preserve internal detail.

HTP is there to help photographers that don't want to handle this themselves, but would rather leave it to the automatic choices in the camera logic.

I don't know about the Canon HTP function in detail, but most other manufacturers include a sort of smart-adaptation setting where the camera only uses the amount of underexposure it thinks it needs to. Shooting a gray house with no specular highlights or point-sources of light on a foggy day - with underexposure - is kind of stupid. That scenario is better served from overexposure and darkening in post - the opposite of the normal HTP function.

In the end, no-one knows better than you what you want from a shot. Learn to adapt to your camera's strong or weak points and adjust your strategy for the session according to that, that's the only way to maximize image quality in all scenarios - with the equipment you have at hand.
Title: Re: ISO 50
Post by: Aglet on January 22, 2013, 06:56:55 PM
You keep saying this but are always unable to post a photo illustrating it, whenever you are asked for one, or the percentage of your images you loose to it, you leave the thread.

Can we see some of these real world images that you consider unusable?

hang in there, I have a busy life - can't spare a lot of time on testing and publishing beyond my initial research for equipment validation.  I already spend too much time here, but it's a good site with some smart folk sharing their knowledge. :)

I now have permission from the subjects to show their photos if I suitably anonymize them.
I also have to look at the multistep workflow I used which was likely something like DPP to TIFF, PS to do some content editing, LR for final finish.  Would not want to make a mistake on what went on there, if possible.

OTOH, the midtone banding examples were from landscape shots w version 1.24 firmware and was where I first noticed the problem that had me stuff the camera in a drawer for a year, miffed at the noise for the $ I spent on it.
With whatever FW i have now, 2.09 I think, i just shot some blank wall last nite and midtone banding is still visible.

is it UNUSABLE?..
if printing large smooth scenes then yes, to me it is. Unless i do some localized NR in PP.
Point is, I should not HAVE to do this with a camera that cost this much when older, cheaper ones like my 40D, did not show this problem.

if a highly textured image, not a problem.
clear blue sky - can be a problem. I'll try find some of that too.

also ran into the metering glitch that sometimes popped up

So yes, I'll start a 5d Mark II bashing topic.  preferably after I sell the darn thing. ;)
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 08:52:29 PM
That they gain a head room and a better reproduction of the high lights if they shoot JPG  and don't know raw, under or over  exposure, post processing etc .

no -- that is not the mechanism that is the  benefit.  how will you explain the HTP mechanism, the effect of exposure, and the number of photons striking the sensor.

It would be so much easier if Mikael would simply admit that he was wrong in stating that the mechanism of HTP has anything to do with altering the amount of light or number of photons hitting the sensor.  But he won't. He will hand-wave, ignore his error, deny that he made statements which are recorded in the thread, respond indirectly, seemingly anything to avoid admitting error.  Some people are like that, there's a neuropsychological term for it, but it's not really relevant. 

Bottom line, Mikael is right about many things, but wrong about this.  Most of us know it.  Fortunately, for those reading this thread who lack a proper understanding of HTP, his mistake concerns the 'how' and not the 'what', and in this case the 'what' is much more important, so the impact of Mikeal's error is low.
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 09:13:02 PM
My dear Neuro, do not tell me I am wrong with out  pointing out what is wrong.
short please
point by point

As you seem so fond of saying: Re-read my earlier posts.

There is no point by point, there is one point.

The 'mechanism of HTP' has nothing to do with altering the amount of light or number of photons hitting the sensor. Yet, no less than 5 times, you stated that it does.
Title: Re: ISO 50
Post by: dlleno on January 22, 2013, 09:13:22 PM
That they gain a head room and a better reproduction of the high lights if they shoot JPG  and don't know raw, under or over  exposure, post processing etc .

no -- that is not the mechanism that is the  benefit.  how will you explain the HTP mechanism, the effect of exposure, and the number of photons striking the sensor.
I have just done that  both by text  and by and illustration. Now its up to you and understand  :)

I don't think you have, Mikael.  Here is the question again:  when the camera's ISO dial is set to something besides 100 (I mean it it is set to 160, 200, 400, or 800 or 1600, etc. etc.) how will you explain the HTT mechanism, the effect upon exposure and the number of photons striking the sensor?
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 09:20:05 PM
That they gain a head room and a better reproduction of the high lights if they shoot JPG  and don't know raw, under or over  exposure, post processing etc .

no -- that is not the mechanism that is the  benefit.  how will you explain the HTP mechanism, the effect of exposure, and the number of photons striking the sensor.
I have just done that  both by text  and by and illustration. Now its up to you and understand  :)

I don't think you have, Mikael.  Here is the question again:  when the camera's ISO dial is set to something besides 100 (I mean it it is set to 160, 200, 400, or 800 or 1600, etc. etc.) how will you explain the HTT mechanism, the effect upon exposure and the number of photons striking the sensor?

My point from earlier, the explanation is 'right' in the same way a broken analog clock is 'right' twice a day. 
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 09:28:43 PM
That they gain a head room and a better reproduction of the high lights if they shoot JPG  and don't know raw, under or over  exposure, post processing etc .

no -- that is not the mechanism that is the  benefit.  how will you explain the HTP mechanism, the effect of exposure, and the number of photons striking the sensor.
I have just done that  both by text  and by and illustration. Now its up to you and understand  :)

I don't think you have, Mikael.  Here is the question again:  when the camera's ISO dial is set to something besides 100 (I mean it it is set to 160, 200, 400, or 800 or 1600, etc. etc.) how will you explain the HTT mechanism, the effect upon exposure and the number of photons striking the sensor?

My point from earlier, the explanation is 'right' in the same way a broken analog clock is 'right' twice a day.
Well, looks like Mikael stands by his Half The Photons theory. Choosing not to communicate on that statement is a communication in itself. Obviously he has a direct channel to the Photon God. So every time he sets his camera to HTP, his request for a reduction in photons is granted by that God...
That is the only logical explanation I can come to...
Over and out
(For now)
Mikael, get some sleep...
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 09:32:50 PM
The time 0324 here in Sweden,
if you Neuro tell another person they are wrong
please point at the errors.

I have. Many times  I'd suggest the late hour is affecting your reading comprehension, but since I've told you several times now, at various times, that's not it.

In previous posts, you accused others of not being able to admit when they are wrong, and questioned our ability to read.  Ironic, isn't it...
Title: Re: ISO 50
Post by: rpt on January 22, 2013, 09:43:45 PM
My G....   You  two Neuroanatomist  and Rpt  don't know the basic how a sensor works, collecting photons and if you are halving the time= go from 100 iso to 200 iso you are halving  the amount of hitting light/photons on the sensor  and  the amount of read out electrons by half.
God night
Good night!
Title: Re: ISO 50
Post by: babiesphotos on January 22, 2013, 10:04:07 PM
The time 0324 here in Sweden,
if you Neuro tell another person they are wrong
please point at the errors.

I have. Many times  I'd suggest the late hour is affecting your reading comprehension, but since I've told you several times now, at various times, that's not it.

In previous posts, you accused others of not being able to admit when they are wrong, and questioned our ability to read.  Ironic, isn't it...

Hey, I am an ex-eastern European.

Where I used to live, there are no interesting careers, not many opportunities to spend creative energy. Nothing changes ever, everyone is looking for a way to kill time, jobs are being held in perpetuality, and businesses are working on inertia. Wherever you are, whoever you are (unless you're researcher at University, or criminal :) there's no opportunity to get immersed in your work. Instead, one spends eternity in arguments with friends that cannot be won, over drinks, or numberless copes of coffee.

I've been 15 years in Canada, and I've changed a lot. And heck, no matter how much I changed, wife still accuses me that sometimes I argue for the sake of arguing :)

So, I'm guessing:
1. Mikael considers all of you friends :)
2. There is no winning argument with him, because for that he'd need to admit that he lost... :)
Title: Re: ISO 50
Post by: Hobby Shooter on January 22, 2013, 10:11:26 PM
so regarding of the subject (motive with no high lights = motive with a small DR) you can overexpose and get a benefit of the over exposure in the shadows

That's great information, thanks! I'll certainly use that once I've got a 6d and am doing tripod macro focus stacks with low dr objects.
I do that regularly with my 5D3 to work around the shadow noise. Results are normally great.

Mikael, question to you, do I understand correct that you mean this is best for low DR pictures ie flatter? I learned through reading a couple of articles to also use this in more high DR situations like taking a street picture with the sun low. I have no experience of not being able to recover details from overexposed highlights. Is there something I'm missing here?

yes a picture turn out flat with a large DR  and which shall be presented in 0-256 levels, but you can adjust the motive so it do not look so flat with different kind of post processing, for example chose some parts and make selective adjustments
Thanks. I will play around with this and see what I can learn.
Title: Re: ISO 50
Post by: J.R. on January 22, 2013, 10:12:48 PM
My apologies as this comes very late in the thread and may seem like a noob question but I am just curious to understand ...

What decides the number of photons that actually hit the sensor? Is it the Aperture and Shutter Speed Or does the ISO play some role in that?

From what I understood previously was that the photons hitting the sensor are the same for the same Aperture and Shutter Speed setting and an increase in the ISO only boosts the signal from the sensor. in other words, it was only when at a particular Aperture Value and Shutter Speed the available light entering the camera (photons) were less that the ISO would require a cranking up to boost signal from the sensor.

After all this discussion abovein the thread, I am quite confused as I don't have a science / engineering background.
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 10:31:19 PM
My G....   You  two Neuroanatomist  and Rpt  don't know the basic how a sensor works, collecting photons and if you are halving the time= go from 100 iso to 200 iso you are halving  the amount of hitting light/photons on the sensor  and  the amount of read out electrons by half.
God night

Seriously?  Mikael, explain to us, step by step, how enabling HTP causes a change in the exposure time or the light/number of photons hitting the sensor.

Try this little experiment:

1. Set camera to M mode with HTP off
2. Set ISO 100, and set aperture and shutter speed to achieve a metered exposure.
3. Enable HTP.

Now, tell us - did the shutter speed change?  Did the aperture change?  If they did not change, how is the amount of light falling on the sensor any different?

I'm sure you'll point out that ISO changed to 200, and the meter shows a 1-stop overexposure.  So, if you now change aperture or shutter speed by a stop to again achieve a metered exposure, that secondary change halves the light. But you did that, not HTP.

Now...that was in the very specific case of ISO 100.  Repeat the above three steps, but in step two, set ISO 200 or higher.  Did the shutter speed change?  Did the aperture change? Try it again in P mode at ISO 200. Did the exposure change?  Explain how in those cases, enabling HTP reduced the amount of light hitting the sensor.  After you've explained that, please explain how a situation that arises in only a very limited set of circumstances, i.e. ISO 100 with an auto-exposure mode (Av, Tv, P) selected represents a general description of the 'mechanism of HTP'. After that, feel free to prove the general accuracy of that broken clock.

Or just ignore these questions, as you ignored dlleno's similar questions.  Answering them would mean acknowledging your mistake, something you're evidently incapable of doing.
Title: Re: ISO 50
Post by: neuroanatomist on January 22, 2013, 10:38:19 PM
My apologies as this comes very late in the thread and may seem like a noob question but I am just curious to understand ...

What decides the number of photons that actually hit the sensor? Is it the Aperture and Shutter Speed Or does the ISO play some role in that?

From what I understood previously was that the photons hitting the sensor are the same for the same Aperture and Shutter Speed setting and an increase in the ISO only boosts the signal from the sensor. in other words, it was only when at a particular Aperture Value and Shutter Speed the available light entering the camera (photons) were less that the ISO would require a cranking up to boost signal from the sensor.

After all this discussion abovein the thread, I am quite confused as I don't have a science / engineering background.

Your previous understanding is absolutely correct.  Only aperture and shutter speed determine the amount of light (number of photons) reaching the sensor.  Any ISO setting other than base ISO (which differs by camera model, is usually in the 60-200 range, and is often not even a user-selectable value, e.g. ISO 80) is gain (analog or digital) applied after the collected photons are converted to electrons and read out from the photosite.

To be blunt, you can safely ignore the drivel that Mikael is spouting about changing ISO somehow affecting the amount of light or number of photons hitting the sensor.
Title: Re: ISO 50
Post by: J.R. on January 22, 2013, 10:49:55 PM
My apologies as this comes very late in the thread and may seem like a noob question but I am just curious to understand ...

What decides the number of photons that actually hit the sensor? Is it the Aperture and Shutter Speed Or does the ISO play some role in that?

From what I understood previously was that the photons hitting the sensor are the same for the same Aperture and Shutter Speed setting and an increase in the ISO only boosts the signal from the sensor. in other words, it was only when at a particular Aperture Value and Shutter Speed the available light entering the camera (photons) were less that the ISO would require a cranking up to boost signal from the sensor.

After all this discussion abovein the thread, I am quite confused as I don't have a science / engineering background.

Your previous understanding is absolutely correct.  Only aperture and shutter speed determine the amount of light (number of photons) reaching the sensor.  Any ISO setting other than base ISO (which differs by camera model, is usually in the 60-200 range, and is often not even a user-selectable value, e.g. ISO 80) is gain (analog or digital) applied after the collected photons are converted to electrons and read out from the photosite.

To be blunt, you can safely ignore the drivel that Mikael is spouting about changing ISO somehow affecting the amount of light or number of photons hitting the sensor.

Thanks for confirming ... It's silly for Mikael to not accept this and defend an incorrect opinion, which in turn misleads others because he does seem to know what he is doing
Title: Re: ISO 50
Post by: sanj on January 22, 2013, 11:40:58 PM
Here you have a old link , there is a comparison between the D7000 and one of my 5dmk2 three years ago
It is up to you or me how to handle large dynamic , but one thing is clear, it is  always better to have large DR , you have more freedom, exposure latitude etc etc, I will close the link after a day


https://picasaweb.google.com/106266083120070292876/DR5dmk2VsD7000

In your test Canon does not look as good as Nikon counterpart. I hope Canon fixes this asap. Talking JUST about sensor.
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 12:00:59 AM
Yeah but if I overexpose a little I quickly loose details in highlights. I do not like that. For my tastes I prefer preserved highlights and richer blacks.

But sometimes the blacks are too dark and I want Canon to give me a little room to open up the blacks when I want to without noise increase. I know it already does give me room, but to my eyes Nikon seems to give bit more.

No stress, life goes on, photos get created. But it is nice to know what the other companies are doing. :)
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 12:47:53 AM

In your test Canon does not look as good as Nikon counterpart. I hope Canon fixes this asap.
That is because he is not exposing for each sensors optimum performance, he is exposing them to the same absolute values, as I keep saying, if your goal is maximum dr then you must overexpose the Canon more, there is a lot more headroom in a Canon file than a Nikon file.

Confused about this. When I shoot I want to expose for what the scene demands rather than what my sensor is comfortable with. Don't u agree?
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 01:05:30 AM

In your test Canon does not look as good as Nikon counterpart. I hope Canon fixes this asap.
That is because he is not exposing for each sensors optimum performance, he is exposing them to the same absolute values, as I keep saying, if your goal is maximum dr then you must overexpose the Canon more, there is a lot more headroom in a Canon file than a Nikon file.

Confused about this. When I shoot I want to expose for what the scene demands rather than what my sensor is comfortable with. Don't u agree?

I don't, unless I'm shooting JPG. For RAW, I go for optimum sensor performance because the image will be post processed anyway and I need as much headroom / DR possible.
Title: Re: ISO 50
Post by: Aglet on January 23, 2013, 01:22:38 AM
So for all your talk you can't post one image that demonstrates the totally unusable files you regularly got from real world shooting the 5D MkII? Amazing...........

I've got more important things to do this week than appease your impatience. :P
In the meantime, start formulating how you will describe that the banding i've experienced with my 5D2 is my fault. ;)  Especially the upper midtone range.  I really want an explanation for that one. [/cheeky]

And then outline how I can fix it with advanced PP skills.  i know you are good at this so hopefully you will share some of this knowledge with us.  I'd like to improve some of the shots that I otherwise like but have these little flaws that annoy me.

When I have time to prep the samples I'll be starting a new thread in this section.

Now I have to go retest a Nikon camera that they've serviced 3 times over 4 months and have made only more problems without addressing the initial one.
I'll give them that, Canon service in my area has been FAR superior to Nikon's.
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 02:05:46 AM

In your test Canon does not look as good as Nikon counterpart. I hope Canon fixes this asap.
That is because he is not exposing for each sensors optimum performance, he is exposing them to the same absolute values, as I keep saying, if your goal is maximum dr then you must overexpose the Canon more, there is a lot more headroom in a Canon file than a Nikon file.

Confused about this. When I shoot I want to expose for what the scene demands rather than what my sensor is comfortable with. Don't u agree?

I don't, unless I'm shooting JPG. For RAW, I go for optimum sensor performance because the image will be post processed anyway and I need as much headroom / DR possible.

JR what does it mean to expose for 'optimum sensor performance'?

I expose for what the scene needs, as to what will make the scene look best. Eg if I am shooting a sunset I would expose for say the clouds and not the sun. Thx JR...
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 03:32:34 AM

[/quote]
To be blunt, you can safely ignore the drivel that Mikael is spouting about changing ISO somehow affecting the amount of light or number of photons hitting the sensor.
[/quote]

Even a child will agree that the amount of light hitting the sensor depends only on f stop/shutter combination. No dispute.
But what I am questioning is that if changing the ISO did not matter, why do we bother setting the ISO? Why does the picture over/under expose if the ISO is not correctly chosen?

ISO kicks in only after the shot is taken, ok. But but it DOES kick in. So should it be factored in while considering the camera calculating total light for that 'click'?

Head starting to spin...
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 05:22:51 AM
Take now  your camera, set the camera on P and  100iso, start to metering  against a white wall, grey card what ever and se what values you get in  time / f-stop   ,  for example 1/60sec F-5,6
Start HTP  The camera now changes to 200iso  and at the same  you get 1 stop shorter time or F-stop.

You have now halving the in falling light /photons to the sensor compared to 100 iso by a shorter exposure time or one more f-stop or both

And Neuro and others, it is you who do not understand how things works
please stop to make your funny- try to understand instead

So, it is your belief that because enabling HTP when in P-mode with ISO 100 set forces a 1-stop change in aperture or shutter speed causing a halving of infalling light, that the mechanism of HTP is a 1-stop change in aperture or shutter speed causing a halving of infalling light?  You have repeatedly stated that HTP works by halving the amount of light/number of photons hitting the sensor.

We are all eagerly awaiting your explanation of how HTP works in P-mode with ISO 200, 400, 125, or any value other than 100, and how it works in M-mode even with ISO 100 set.  If you can demonstrate that enabling HTP always results in a 1-stop change in aperture or shutter speed, you are correct that HTP works by reducing the amount of light hitting the sensor. If you cannot, you are wrong and should admit it.
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 05:36:06 AM
Even a child will agree that the amount of light hitting the sensor depends only on f stop/shutter combination. No dispute.
But what I am questioning is that if changing the ISO did not matter, why do we bother setting the ISO? Why does the picture over/under expose if the ISO is not correctly chosen?

ISO kicks in only after the shot is taken, ok. But but it DOES kick in. So should it be factored in while considering the camera calculating total light for that 'click'?

Head starting to spin...

Not all children, seemingly.

Of course ISO should be considered. The analog gain is applied before the signal off the sensor is digitized, so it's 'baked' into the RAW file.  J.R.'s confusion was caused by statements in this thread suggesting that changing ISO directly alters the amount of light hitting the sensor (which it does not, although it can do so indirectly, in an auto-exposure mode, P/Av/Tv), or that changing ISO alters the number of photons able to be captured, e.g. reducing the full well capacity, which is also not true.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 05:38:04 AM

Are you  gays serious

Take now  your camera, set the camera on P and  100iso, start to metering  against a white wall, grey card what ever and se what values you get in  time / f-stop   ,  for example 1/60sec F-5,6
Start HTP  The camera now changes to 200iso  and at the same  you now get 1 stop shorter time or F-stop.

You have now halving the in falling light /photons to the sensor compared to 100 iso by a shorter exposure time or one more f-stop or both

And Neuro and others, it is you who do not understand how basic  things works and Im sorry that thou do not know  basic knowledge
And please  Neuro stop to make your funny on my behalf,  that Im writing drivel etc - try to understand instead .



First things first ... Please don't call us "gays". I guess it just might be a typo but nevertheless this is something I have to refute as it is typed out in bold.

If you read my above post, I specifically mentioned that as per my understanding the photons could be halved only by changing the shutter speed and / or the aperture - which is what you are also implying.

Also, I can agree that in the P mode, the photons hitting the sensors would be halved - but this will happen only if you started at ISO 100 in the first place - it is also of note that the halving of the photons happens only because of the in-camera override.

I also tried this just now ... Start out at ISO 400, meter a scene ... Now enable HTP ... Nothing changes whatsoever.

Thus concluded ... HTP does not change the number of photons hitting the sensor. If you we're to start out at ISO 100 though,the camera will automatically change the ISO, aperture and/or shutter speed when you are on ISO 100.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 05:48:23 AM

JR what does it mean to expose for 'optimum sensor performance'?

I expose for what the scene needs, as to what will make the scene look best. Eg if I am shooting a sunset I would expose for say the clouds and not the sun. Thx JR...

Sorry for the confusion, What I meant was that for some situations where I feel the scene warrants shadow recovery, it would be better to overexpose the shot slightly and adjust the highlights in post processing rather than lift the shadows.

The Sun is a bad example ... I guess you put it there trying to make it impossible for me to answer ;) an attempt at the answer would be that it all depends on what you shoot and your choice ... I feel that ETTR works for me. YMMV
Title: Re: ISO 50
Post by: marinien on January 23, 2013, 05:49:17 AM
To whom is HTP for? To people who are using the camera in JPG mode and automatic mode to get better reproduction of contrasty motives , raw people with little knowledge understand under exposing and post processing

I will call you men  not gays , is that more proper?

Oh, Mikael, you forgot ISO100, didn't you?  ;D
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 05:51:02 AM
@ Neuro. Ok I now learned that no matter what ISO is selected, the sensor collects equal amount of light but processes it differently depending upon the ISO setting.
Cool.
Thx.
I have not yet pieced it together in my mind how this causes blown highlights at 50 ISO, but since I do not intend to use 50 iso anymore, I will let this pass... Why bother taxing my not so technical mind... :)
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 05:51:47 AM
To whom is HTP for? To people who are using the camera in JPG mode and automatic mode to get better reproduction of contrasty motives , raw people with little knowledge understand under exposing and post processing

I will call you men  not gays , is that more proper?

Agree on the first part.

"Gays" means homosexuals in my part of the world ... I thought you meant "guys" which would have been correct - I mentioned as much in my above post where I said it could have been a typo.
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 05:52:57 AM
I have just done that.

and read the suedes answer at page 12 , he handles english much better than me


The suede:
Yes, compared to using the camera at ISO100, turning HTP on makes the camera expose for at least ISO200, which is a full stop difference in photometric exposure. A halving of the number of photons captured in a normal case camera-choice automatic exposure. True. But that's the intention and planned execution of the function, so that particular point needs no further discussion in my view.

Do you understand that the case of enabling HTP when at ISO 100 in a an auto-exposure mode causing a halving of the number of photons is a unique case applicable only when at ISO 100 in a an auto-exposure mode?

Several times, you made statements like:

mechanism behind HTP...
In HTP  the sensor  has now been hit by  less light/photons

and:

HTP. it is a halving of infaling light

If the 'mechanism of HTP' is to reduce the amount of light hitting the sensor, then that mechanism must apply generally, not only in the unique case of being at ISO 100 in an auto-exposure mode when HTP is enabled.

Since your explanation of the 'mechanism of HTP' is not applicable at most ISO settings in all exposure modes, your explanation is wrong.  It really is just that simple.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 05:57:40 AM

I have not yet pieced it together in my mind how this causes blown highlights at 50 ISO, but since I do not intend to use 50 iso anymore, I will let this pass... Why bother taxing my not so technical mind... :)

Same here - ISO 50 shall be used by me only in case I don't have a NDX at hand.
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 06:03:48 AM
I have not yet pieced it together in my mind how this causes blown highlights at 50 ISO, but since I do not intend to use 50 iso anymore, I will let this pass... Why bother taxing my not so technical mind... :)

Setting ISO 50 'causes' blown highlights only because you change aperture or shutter speed to maintain a metered exposure (relative to ISO 100).  The ISO change doesn't directly blow the highlights (if you change from ISO 100 to 50 in M-mode and then press the shutter, your meter will show a stop of underexposure).  But when you change aperture/shutter to let in more light, that can blow highlights that would not blow at ISO 100.

Point being, if you're at ISO 100 with almost-blown highlights and need a slower shutter or wider aperture, ISO 50 won't save your highlights - you need an ND filter in that case.
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 06:04:29 AM
@ Neuro. Ok I now learned that no matter what ISO is selected, the sensor collects equal amount of light but processes it differently depending upon the ISO setting.
Cool.
Thx.
I have not yet pieced it together in my mind how this causes blown highlights at 50 ISO, but since I do not intend to use 50 iso anymore, I will let this pass... Why bother taxing my not so technical mind... :)

what do we then have shutter speeds and different F-stops for?
I think the coin is falling down

Please explain more Mikael. Did not understand your comment. Thx.
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 06:06:09 AM

JR what does it mean to expose for 'optimum sensor performance'?

I expose for what the scene needs, as to what will make the scene look best. Eg if I am shooting a sunset I would expose for say the clouds and not the sun. Thx JR...

Sorry for the confusion, What I meant was that for some situations where I feel the scene warrants shadow recovery, it would be better to overexpose the shot slightly and adjust the highlights in post processing rather than lift the shadows.

The Sun is a bad example ... I guess you put it there trying to make it impossible for me to answer ;) an attempt at the answer would be that it all depends on what you shoot and your choice ... I feel that ETTR works for me. YMMV

Ok we work the same way it seems. Even though I do not know what ETTR or YMMV mean. :)
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 06:09:27 AM
neuro wrote

Do you understand that the case of enabling HTP when at ISO 100 in a an auto-exposure mode causing a halving of the number of photons is a unique case applicable only when at ISO 100 in a an auto-exposure mode?

yes I do, to create a head room which is described earlier

So, IF you understand that enabling HTP when at ISO 100 in an auto-exposure mode is a unique case only applicable at ISO 100 in an auto-exposure mode, THEN it follows that your explanation of the general mechanism of HTP as a halving of infalling light is WRONG.

Will you admit that?
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 06:09:38 AM
@Micheal: Do you mean "the penny dropped"?  ;D

So I am right? But is that not what Neuro has been saying and you disagreeing? Where lies MY confusion...?

Thx guy
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 06:13:39 AM

Ok we work the same way it seems. Even though I do not know what ETTR or YMMV mean. :)

ETTR ... Expose To The Right
YMMV ... Your Mileage May Vary
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 06:17:19 AM
ETTR ... Expose To The Right
YMMV ... Your Mileage May Vary

TMBSITT ... Too Much BS In This Thread

I trust I don't need to spell out what BS means...   ;)
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 06:17:30 AM

[/quote]
Setting ISO 50 'causes' blown highlights only because you change aperture or shutter speed to maintain a metered exposure (relative to ISO 100). Not clear as I am still exposing correctly for both ISO.

The ISO change doesn't directly blow the highlights (if you change from ISO 100 to 50 in M-mode and then press the shutter, your meter will show a stop of underexposure).  Agree, basic even for me.

But when you change aperture/shutter to let in more light, that can blow highlights that would not blow at ISO 100. Dont understand why. As I am still exposing correctly.

Point being, if you're at ISO 100 with almost-blown highlights and need a slower shutter or wider aperture, ISO 50 won't save your highlights - you need an ND filter in that case. Agree. But I would attempt ISO 50 not to save the hightlights but to get even lesser noise.

[/quote]
Title: Re: ISO 50
Post by: MarkII on January 23, 2013, 06:37:07 AM
So, to summarise, what is happening is:

Camera Setting     Image EXIF Reports     Actual sensor gain     Actual metering gain     net effect     
ISO 50ISO 50ISO 100ISO 50Brighter shadows; blown highlights
ISO 100ISO 100ISO 100ISO 100Normality
ISO 200 HTPISO 200ISO 100ISO 200Highlights preserved; shadows burned

ie - ignoring any small shifts due the possibility that the 'native sensor base ISO is not exactly ISO100 - the only differences between the three modes are the metering and the subsequent processing to correct for the metering error.

If you shoot JPEG, the camera automatically compensates for the difference between the sensor and metering gain. If you shoot RAW, the file contains a flag that allows your RAW processor to do this. You can achieve a similar effect by simply using the exposure compensation setting and correction later - though the in-camera options will give better quality if you shoot JPEG.

The only real difference is in the exposure, metering and post processing. The metering gain changes really do mean that the number of photons hitting the sensor are affected by the mode setting - relative to the actual sensor ISO gain setting [edited for clarity].

Can anyone point out where this is incorrect?
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 07:19:42 AM
neuro wrote

Do you understand that the case of enabling HTP when at ISO 100 in a an auto-exposure mode causing a halving of the number of photons is a unique case applicable only when at ISO 100 in a an auto-exposure mode?

yes I do, to create a head room which is described earlier

So, IF you understand that enabling HTP when at ISO 100 in an auto-exposure mode is a unique case only applicable at ISO 100 in an auto-exposure mode, THEN it follows that your explanation of the general mechanism of HTP as a halving of infalling light is WRONG.

Will you admit that?

even here you are missing the point, or do not understand, all started with that I explained it must be created a head room by under expose 100iso. Halving the read out electrons , halving the amount of light who are hitting the sensor. Some of you  " cough cough " start to argue against that. This is way the camera are changing from 100 iso to 200iso and make the exposure time shorter or 1 more F-stop from example F-4 to 5,6.= cutting infallng light by one stop  to hit the sensor
From 200iso and up the head room is created, and for evey iso stop or step  i the head room will be one stop  larger= the photons who are hitting the sensor is halving each  iso step because of shorter  exposure time/  or one more f-stop  aperture  and the  gain is increased  in every step / stop but only to the limit that there are still a head room left , then in the camera the software compensate  with another curve and roling softer in the high lights .


So, your actual answer to my question is, "No, I will not admit that I am wrong."
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 07:25:05 AM
Yes, please go back to step one and explain how, at ISO 400 (or, in fact, any ISO other than 100), enabling HTP results in Half The Photons hitting the sensor.

We're waiting.
Title: Re: ISO 50
Post by: marinien on January 23, 2013, 08:12:15 AM
Yes, please go back to step one and explain how, at ISO 400 (or, in fact, any ISO other than 100), enabling HTP results in Half The Photons hitting the sensor.

We're waiting.
it doesn't, there already a head room created by halving  the signal / e  at 200iso  from 100iso , and agin a halving  from 200 to 400iso  and from 400 to 800 etc  etc , se earlier answer

Now I have a Sigma 35/1,4 to pick up and test/ compare to my canon 35/1.4

Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 08:19:17 AM
TMBSITT  :'(
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 09:16:35 AM
Yes, please go back to step one and explain how, at ISO 400 (or, in fact, any ISO other than 100), enabling HTP results in Half The Photons hitting the sensor.
it doesn't

Finally.  So, before you stated that the mechanism of HTP was a reduction by half in the amount of light /number of photons hitting the sensor.  Now, you are finally admitting that's not true.

Perhaps not quite the mea culpa we could have expected, but it'll have to do.

Enjoy the Sigma 35/1.4 - by all accounts, it's an excellent lens and I expect you'll find it trumps the Canon 35L in many ways.
Title: Re: ISO 50
Post by: Meh on January 23, 2013, 09:18:39 AM
So, your actual answer to my question is, "No, I will not admit that I am wrong."

Why would he, he now has his "special case" to yammer on about to avoid dealing with his mistakes.  The most entertaining part is that the special case was suggested by someone else as a possible explanation for what he meant and now he adopts it like it's what he was talking about all along.

ETTR ... Expose To The Right
YMMV ... Your Mileage May Vary

TMBSITT ... Too Much BS In This Thread

I trust I don't need to spell out what BS means...   ;)

You should have mentioned.... Too much NPD in this thread
Title: Re: ISO 50
Post by: rpt on January 23, 2013, 10:23:01 AM
          _______
         /              \
        /                \
       /                  \
      |       R I P     |
      |                    |
      |                    |
^^^~~~~^^^~~~^^^

                   
Title: Re: ISO 50
Post by: sanj on January 23, 2013, 10:23:20 AM
tre men waiting for a new canon 7d MK2 ?
se you

Hahahaha. Must say this is funny..... really. Good one!
Title: Re: ISO 50
Post by: dlleno on January 23, 2013, 10:29:12 AM
finally a breakthrough.  I really tried guys I really did.  I tried to get mikael to answer a very specific question and he avoided it with the great skill of an inkfish. 
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 12:28:03 PM
So who am I, Oprah?!?   :o
Title: Re: ISO 50
Post by: TheSuede on January 23, 2013, 12:47:23 PM
Quote from: neuroanatomist

Do you understand that the case of enabling HTP when at ISO 100 in a an auto-exposure mode causing a halving of the number of photons is a unique case applicable only when at ISO 100 in a an auto-exposure mode?
yes I do, to create a head room which is described earlier

So, IF you understand that enabling HTP when at ISO 100 in an auto-exposure mode is a unique case only applicable at ISO 100 in an auto-exposure mode, THEN it follows that your explanation of the general mechanism of HTP as a halving of infalling light is WRONG.

Will you admit that?
I take it the answer was "yes".

I would think this concludes this argument series.
As far as I can understand from the [considerably more than!] somewhat confused string of comments in this thread, no party is/was actually strictly incorrect, since both parties are constantly avoiding the "Yes, but I'm talking about...." pretext of the responding posts.

Though I cannot help but feel that at least one side of the argumentation has gone out of it's way to not read the intended meaning of the "opposite side's" statements and argumentation. And the undertone of constant provocation isn't very unflattering.

This isn't meant to be condescending towards Mikael - since he is well aware of both his light dyslexia and his short temper - but this thread feels like a kindergarten playground where a pack of children are trying to provoke a dyslectic kid with very short temper into doing something stupid and aggressive while the teachers are watching - so they can say that "he started the violence!" and point the blame to him - and get him expelled. As I said: Not a very flattering impression.

In the end, from a factual PoV:


Feel free to add constructive criticism, or point out any error(s). But be very ashamed if this post is considered OT and erased.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 01:18:41 PM

This isn't meant to be condescending towards Mikael - since he is well aware of both his light dyslexia and his short temper - but this thread feels like a kindergarten playground where a pack of children are trying to provoke a dyslectic kid with very short temper into doing something stupid and aggressive while the teachers are watching - so they can say that "he started the violence!" and point the blame to him - and get him expelled. As I said: Not a very flattering impression.


Not really, IMHO it was just a matter of a very simple,yes or no. Not everyone is very good at the technical aspects and it becomes confusing when contradictory information is provided.

I believe that Mikeal is astute technically and knows what he is doing when it comes to cameras and their components ... But he categorically maintained that HTP will reduce the photons to half regardless of the base ISO setting and hence the confusion. Maybe you understand what he has been writing all along but then there are lesser mortals (such as me) who ponder whether or not what they have learnt (over the limited time they have been shooting) was correct.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 01:28:48 PM
finally a breakthrough.  I really tried guys I really did.  I tried to get mikael to answer a very specific question and he avoided it with the great skill of an inkfish.

If you do not understand  the answers I have presented  it is nothing I can do about your problem= to understand, but do not make you funny on my behalf, it is time for you, Neuro and others to study the subject. In plain english, you gentleman seems not to have  a clue about what I have answer you many times,  head room  , the relation of time/f-stop and signal photons collecting / charge , and signal amplifying. I hope you others members who are not a member of a particular  persons fan club have learn something
Thank you the_ suede that you are supporting me.

Thanks Mikael. If you see my earlier post, that is what I was doing ... Studying the subject. Now, I always understood that the photons will be halved if the Aperture/Shutter speed is changed by 1 stop. But going by the thread I somehow got the impression that changing the ISO (what happens in HTP) automatically changes the amount of light hitting the sensor - something that Neuro, as well as yourself confirmed, Doesn't happen!
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 01:34:19 PM

Then you have  learn something new today?

Of course YES! That the ISO 50 is and HTP are basically useless if you shoot raw and post process. also, a basic understanding of how the sensor works.

Unless you know what's wrong you never know what is right
Title: Re: ISO 50
Post by: neuroanatomist on January 23, 2013, 01:41:47 PM
In the end, from a factual PoV:

  • HTP does not in any case UNLESS the one-off case where the starting point is ISO100 lower absolute photometric exposure. At set ISOs 200-800 it does however increase the electronic noise pollution in the finished image somewhat in Canon cameras.
  • Exposure is exposure is exposure, and exposure sets the photon noise level in the image. It's set by the scene light emittance modulated by shutter speed and lens T-stop (aperture + losses), and actually also for all practical considerations: QE of the sensor. Not by ISO - though the ISO setting can change aperture and/or shutter speed when the camera is in auto- mode (anything but "M" mode), it's a secondary effect. ISO changes setting, setting changes exposure.
  • ISO in digital cameras is a translating factor between exposure (exposure x QE = cell charge) and raw file ADU value.
  • The amount of headroom available in a camera can NEVER be higher than when the camera is used on base ISO (ISO100 in the case discussed here) - Since the highest DR is always at base ISO, unless the construction is seriously flawed (actually totally botched!). This means that ISO200 + HTP has the same 'potential' headroom, since the actual physical amplification is set at ISO100, not 200
  • ISO50 (or more generally "lower than actual base ISO") settings are useless for raw shooters, but may be of some use for jpg shooters.

The only point I'd add to your astute summary is to correct the following:

• HTP does not in any case UNLESS the one-off case where the starting point is ISO100 lower absolute photometric exposure.

Assuming you're in an auto-exposure mode where the camera can change the aperture/shutter speed, enabling HTP lowers actual exposure any time the selected ISO is lower than 200, i.e. by 1/3-stop if ISO 160 is set, by 2/3-stop if ISO 125 is set, and by 2-stops if ISO 50 is set.  But only at ISO 100 is the amount of lowering equal to one stop, i.e. 'half the photons'.
Title: Re: ISO 50
Post by: MarkII on January 23, 2013, 01:46:03 PM

This isn't meant to be condescending towards Mikael - since he is well aware of both his light dyslexia and his short temper - but this thread feels like a kindergarten playground where a pack of children are trying to provoke a dyslectic kid with very short temper into doing something stupid and aggressive while the teachers are watching - so they can say that "he started the violence!" and point the blame to him - and get him expelled. As I said: Not a very flattering impression.


Not really, IMHO it was just a matter of a very simple,yes or no. Not everyone is very good at the technical aspects and it becomes confusing when contradictory information is provided.

I believe that Mikeal is astute technically and knows what he is doing when it comes to cameras and their components ... But he categorically maintained that HTP will reduce the photons to half regardless of the base ISO setting and hence the confusion. Maybe you understand what he has been writing all along but then there are lesser mortals (such as me) who ponder whether or not what they have learnt (over the limited time they have been shooting) was correct.

The quality of the discussion is terrible.

What makes this worse is that I think you can argue that both Neuro and Mikeal are correct. You view ISO200+HTP as ISO200 (the metering sensitivity) with a modified sensor sensitivity, or you can view it as ISO100 (the sensor sensitivity) with a modified exposure. You also need to keep in mind that not everyone is an expert in English.

A lot of hot air about nothing.
Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 01:50:54 PM

This isn't meant to be condescending towards Mikael - since he is well aware of both his light dyslexia and his short temper - but this thread feels like a kindergarten playground where a pack of children are trying to provoke a dyslectic kid with very short temper into doing something stupid and aggressive while the teachers are watching - so they can say that "he started the violence!" and point the blame to him - and get him expelled. As I said: Not a very flattering impression.


Not really, IMHO it was just a matter of a very simple,yes or no. Not everyone is very good at the technical aspects and it becomes confusing when contradictory information is provided.

I believe that Mikeal is astute technically and knows what he is doing when it comes to cameras and their components ... But he categorically maintained that HTP will reduce the photons to half regardless of the base ISO setting and hence the confusion. Maybe you understand what he has been writing all along but then there are lesser mortals (such as me) who ponder whether or not what they have learnt (over the limited time they have been shooting) was correct.

The quality of the discussion is terrible.

What makes this worse is that I think you can argue that both Neuro and Mikeal are correct. You view ISO200+HTP as ISO200 (the metering sensitivity) with a modified sensor sensitivity, or you can view it as ISO100 (the sensor sensitivity) with a modified exposure. You also need to keep in mind that not everyone is an expert in English.

A lot of hot air about nothing.


Apologies ... English is not my first language either
Title: Re: ISO 50
Post by: dlleno on January 23, 2013, 02:25:46 PM
language problems, aside, when all parties are interested in finding truth, success can still happen.  The problem here is that truth wasn't discovered during the process.  it was hammererd out with great pain.  this what disapointed me about the discussion was that it did not converge.  instead it went  something like this:

HTP halves the number of photons hitting the sensor
no thats not true all the time
yes it is true, see my ISO100 example
ok for the special case of ISO 100 that is true, what about the other cases?
the number of photons is halved, see my ISO100 example
no that can't be true:  when ISO is 200 or 400 or 160, the number of photons is not halved
yes it is true, half the photons strike the sensor, see my ISO100 example
be specific:  how does HTP work with the ISO dial is set to 400.  is the number of photons halved?
HTP benefits jpg shooters
you need to say that the number of photons is not halved when the ISO dial is set too 400
no I won't please see my ISO 100 example.
Don't you see that when ISO is set to 400, HTP does not halve the number of photons
I've been saying that all along.

   
clear, precise technical explantions are more difficult when language is a issue, but they can still happen, and I hope they do, in the future.  I for one was frustrated becasue we could not get the conversation to converge on the true technical mechanism underlying HTP that would happen in the  majority of the cases and for the majority of togs, i.e. those who have not glued their ISO dial to "100".  suede I'm glad you finally summarized it.  whew

Title: Re: ISO 50
Post by: J.R. on January 23, 2013, 02:37:03 PM
Time for me to get some sleep with some hope that I won't be entertaining M/s ISO 50 or M/s HTP tonight. Won't be tempted to revisit this thread either ... It's taken it's toll on me  :'(
Title: Re: ISO 50
Post by: dlleno on January 23, 2013, 02:59:26 PM
finally a breakthrough.  I really tried guys I really did.  I tried to get mikael to answer a very specific question and he avoided it with the great skill of an inkfish.

If you do not understand  the answers I have presented  it is nothing I can do about your problem, but do not make you funny on my behalf, it is time for you, Neuro and others to study the subject. In plain english, you gentleman seems not to have  a clue about what I have answer you many times,  head room  , the relation of time/f-stop and signal photons collecting / charge , and signal amplifying. I hope you other members who are not a member of a certain  persons fan club have learn something
Thank you the_ suede that you are supporting me.

most of us get all of that Mikael, we understand these concepts and your explanations were accepted.  I just couldn't correlate the "please see my ISO 100 example" approach to the case where the ISO dial is set to 400. 

My nature is the relentless persuit of technical precision and accuracy, which has nothing to do with membership into any presumed club, a comment which I find rude and uncalled for.  my suggestion is that if you relentlessly persue technical and linguistic precision in a conversation,  the personal nonesense disapears and you will be free to point out what is fact because it is fact, not because you or anyone else said it.   With the depth of understanding you have demonstrated,  I would say in the future  just please listen more carefully to the question being asked.

I will admit that my comment about the inkfish was condecending so you have my apologies for that.   Just please in the future be open to the technically-motivated goals of others and try to answer very specific questions with technical precision.  I realize English is not your primary language, and in fact your English is very good I would say, considering all of that.  I just found that for some reason you were unable to respond to a very specific question with a very specific answer, causing the whole  conversation to go crazy.
Title: Re: ISO 50
Post by: seekthedragon on January 23, 2013, 04:45:35 PM
Hi everyone!

This thread seems to be quite interesting, as I would really like to know more about HTP. However, would you kindly do me a favor and summarize the conclusion of this argument?  I tried to read it, but sometimes, it becomes quite pointless, and my English is just too poor to understand all the pages.

Your Sincerely

David
Title: Re: ISO 50
Post by: dlleno on January 23, 2013, 04:51:12 PM
Below is the best single summary to date


In the end, from a factual PoV:

  • HTP does not in any case UNLESS the one-off case where the starting point is ISO100 lower absolute photometric exposure. At set ISOs 200-800 it does however increase the electronic noise pollution in the finished image somewhat in Canon cameras.
  • Exposure is exposure is exposure, and exposure sets the photon noise level in the image. It's set by the scene light emittance modulated by shutter speed and lens T-stop (aperture + losses), and actually also for all practical considerations: QE of the sensor. Not by ISO - though the ISO setting can change aperture and/or shutter speed when the camera is in auto- mode (anything but "M" mode), it's a secondary effect. ISO changes setting, setting changes exposure.
  • ISO in digital cameras is a translating factor between exposure (exposure x QE = cell charge) and raw file ADU value.
  • The amount of headroom available in a camera can NEVER be higher than when the camera is used on base ISO (ISO100 in the case discussed here) - Since the highest DR is always at base ISO, unless the construction is seriously flawed (actually totally botched!). This means that ISO200 + HTP has the same 'potential' headroom, since the actual physical amplification is set at ISO100, not 200
  • ISO50 (or more generally "lower than actual base ISO") settings are useless for raw shooters, but may be of some use for jpg shooters.

Feel free to add constructive criticism, or point out any error(s). But be very ashamed if this post is considered OT and erased.