Messages

541

EOS Bodies - For Stills / Re: Is Full Frame sharper than APS-C? My answer here

« on: January 20, 2013, 11:58:16 PM »

Let us say that you have a APS sensor 24Mp with the same S/N as a  24Mp 24x36 sensor then it is an optical question, it is hard to make a APS  lens 1,5 1,6 times better which is require compared to 24x36mm lens.

This is incorrect.

Because there will be less absolute magnification for a same-sized print with the larger format, even if the sensors have the same pixel dimensions, the larger format will be sharper and have less noise. Again, always assuming all else is comparable, including a longer focal length lens for the larger format.

Cheers,

b&

542

EOS Bodies - For Stills / Re: ISO 50

« 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&

543

EOS Bodies - For Stills / Re: Is Full Frame sharper than APS-C? My answer here

« on: January 20, 2013, 05:57:45 PM »

Once again, all else is clearly not always equal. If all you've got is a 300mm lens and you want to shoot the full disc of the moon, yes, of course, you're going to get better results from that lens with a 7D than a 5DIII. But the guy next to you with a 5DIII and a 1200mm f/5.6 is going to get an image of the moon that puts yours with your 7D to shame. And the guy the next hill over, the one with a 32" Dobsonian? Well....

yeah..... but is the guy on the last hill hand-holding the 32" Dobsinian? And if he is, who's going to argue with him?

The <a href="http://hubblesite.org/">gang down south</a> might be able to give him a good run for the money....

b&

544

EOS Bodies - For Stills / Re: ISO 50

« on: January 20, 2013, 05:54:22 PM »

I give up....

b&

545

1D X Sample Images / Re: Rocket Launch shoot with Canon 1dx

« on: January 20, 2013, 05:52:21 PM »

Oh -- one more thing.

I think I would have gone for a portrait orientation, pulled back so you had the same field of view and framing at the bottom, but a bunch of black sky above the rocket. There might also be some interesting compositional opportunities with an off-center framing, perhaps with just the towers to the right. It'd also be neat to get a bit more elevation for yourself for the shot, to be able to include the launch pad in the shot rather than have it be obscured by that building. Indeed, if not too unsafe, the roof of that building would be the perfect spot....

Here's hoping you have lots and lots of opportunities to experiment with this...sure wish I did....

Cheers,

b&

546

1D X Sample Images / Re: Rocket Launch shoot with Canon 1dx

« on: January 20, 2013, 05:45:15 PM »

That's got to be a seriously fun gig, and an amazing experience in person.

The shot works, but I think I'd go a lot brighter -- as in, at least a few stops brighter. I'm guessing the rocket is moving pretty slow that close to the ground. I don't see any motion blur at 1/1000s and not much noise at ISO 800 and no signs of too shallow a depth of field at f/6.3, so you had plenty of room to brighten it up.

I've taken the liberty of fooling with it in ACR; attached is my rough interpretation. Obviously, starting with the original raw file instead of a JPEG would give better results.

Cheers,

b&

547

EOS Bodies - For Stills / Re: ISO 50

« 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&

548

EOS Bodies - For Stills / Re: ISO 50

« 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:

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&

549

EOS Bodies - For Stills / Re: Is Full Frame sharper than APS-C? My answer here

« on: January 20, 2013, 01:34:35 PM »

We could not tell any difference, apart from the DoF.

I'm actually not at all surprised. You even could have equalized the DoF by shooting the 5DII at f/11 and ISO 200.

In good light with good glass at small apertures, you'd have to be printing large and looking very critically to tell the difference.

But in dim light, or if you need to stretch the dynamic range by pulling up the shadows...that's when the 5DII is going to start to pull away. Or if you're making prints bigger than 24" x 36".

And still, poor technique can easily obliterate the differences.

b&

550

EOS Bodies - For Stills / Re: ISO 50

« 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&

551

EOS Bodies - For Stills / Re: Is Full Frame sharper than APS-C? My answer here

« on: January 20, 2013, 01:08:36 PM »

There are certain situations where a crop delivers higher resolution than a FF with the same lens (even disregarding DoF, AF and the corners). Roger M. Clark has nice shots of the moon with the 5D2 and the 7D that show this:

www.clarkvision.com/articles/digital.sensor.performance.summary

When I wrote, "All else being equal, the larger the format, the better the image quality," there was obviously a bit of shorthand going on. Particularly, to maintain the same field of view with a larger format, you need a longer focal length. Just as you wouldn't compare a P&S with an 8mm lens to a 5DIII with an 8mm lens, you really can't compare a 7D with a 300mm lens to a 5DIII with a 300mm lens -- even if you can physically mount the same lens to both cameras. Rather, you'd compare that P&S with an 8mm lens to a 5DIII with a 50mm lens, and you should compare the 7D with a 300mm lens to a 5DIII with a 500mm lens -- native, in all cases, not with extenders.

And you will, indeed, get substantially better images (with comparable framing) from a 5DIII with a 500mm lens than a 7D with a 300mm lens. That an uncropped image from a 7D with a 300mm lens is superior to a cropped image with a 300mm lens is no more surprising than that slicing away all of an 8x10 negative shot with a 300mm lens but for a 1" x 1.5" rectangle results in a worse image than you'd get from a 135 frame with a 35mm lens.

Once again, all else is clearly not always equal. If all you've got is a 300mm lens and you want to shoot the full disc of the moon, yes, of course, you're going to get better results from that lens with a 7D than a 5DIII. But the guy next to you with a 5DIII and a 1200mm f/5.6 is going to get an image of the moon that puts yours with your 7D to shame. And the guy the next hill over, the one with a 32" Dobsonian? Well....

Cheers,

b&

552

EOS Bodies - For Stills / Re: ISO 50

« 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&

553

EOS Bodies - For Stills / Re: Is Full Frame sharper than APS-C? My answer here

« on: January 20, 2013, 10:28:24 AM »

All else being equal, especially including the final print size (a factor which often gets ignored and confused with respect to pixel peeping), the larger the format, the better the image quality in every aspect. That includes sharpness as well as noise / grain as well as dynamic range as well as anything else you care to mention.

Of course, all else is never actually equal, which is why it's important to compare complete systems. Neoruanatomist made that point; better theoretical maximum image quality is useless if you can't properly operate (in the specific case, focus) the equipment.

There's another factor to consider. Image quality with even entry-level DSLRs and kit lenses is superlative. Anything going to the Web, 4x6 prints, and even 8x10 prints...there's no practical real-world image quality difference between a Rebel and medium format (with the exception that you can more easily get a greater amount of background separation with the larger format).

Once you're printing on a machine that won't sit on your desktop, though, the difference between the different formats starts to become apparent. You can make a great roadside billboard with a Rebel and a kit lens, but walk up to a pair of door-sized fine art prints, one made with said Rebel and the other with an 8x10 view camera, and even your half-blind great uncle will be able to tell the difference.

Cheers,

b&

554

EOS Bodies - For Stills / Re: ISO 50

« 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&

555

EOS Bodies - For Stills / Re: ISO 50

« 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.

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.

(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&