July 26, 2014, 03:12:34 AM

Author Topic: ISO 50  (Read 34719 times)

Marsu42

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Re: ISO 50
« Reply #120 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

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Re: ISO 50
« Reply #120 on: January 22, 2013, 12:42:32 PM »

J.R.

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Re: ISO 50
« Reply #121 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

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rpt

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Re: ISO 50
« Reply #122 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... ::)

RLPhoto

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Re: ISO 50
« Reply #123 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.

TheSuede

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Re: ISO 50
« Reply #124 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...) :)

neuroanatomist

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Re: ISO 50
« Reply #125 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!
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Don Haines

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Re: ISO 50
« Reply #126 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.
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Re: ISO 50
« Reply #126 on: January 22, 2013, 02:43:01 PM »

dlleno

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Re: ISO 50
« Reply #127 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? 

dlleno

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Re: ISO 50
« Reply #128 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?

dlleno

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Re: ISO 50
« Reply #129 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.

TheSuede

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Re: ISO 50
« Reply #130 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.

Aglet

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Re: ISO 50
« Reply #131 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. ;)

neuroanatomist

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Re: ISO 50
« Reply #132 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.
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Re: ISO 50
« Reply #132 on: January 22, 2013, 08:52:29 PM »

neuroanatomist

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Re: ISO 50
« Reply #133 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.
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dlleno

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Re: ISO 50
« Reply #134 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?

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Re: ISO 50
« Reply #134 on: January 22, 2013, 09:13:22 PM »