For owners of 1DIII with no mega-pixel peeping allergy only ;-)

[Peter Ruevski]

Hi all,

There is something I would like to know about the 1DIII and since I do not have one (for now) I have a "strange" request. I would be grateful if someone who has one does the following test:
1. Take the lens off and put a body cap on.
3. Take one photo at all possible ISO settings using 1/100s shutter speed (all pictures will be pitch black).
4. Upload the the raw files somewhere and post the link (or PM me - I can come up with FTP space or a Gmail account)

Regards,
Peter

P.S. Whole ISO settings (100, 200, 400 etc.) only would be gladly accepted too, but I prefer all of them.
P.P.S. Tell me what the temperature was if you know it.

[John Sheehy]

Originally Posted by Peter Ruevski

Hi all,

There is something I would like to know about the 1DIII and since I do not have one (for now) I have a "strange" request. I would be grateful if someone who has one does the following test:
1. Take the lens off and put a body cap on.
3. Take one photo at all possible ISO settings using 1/100s shutter speed (all pictures will be pitch black).
4. Upload the the raw files somewhere and post the link (or PM me - I can come up with FTP space or a Gmail account)

There really should be a repository somewhere of stuff like this. All the RAW sample sites have sharply focused images without real black; it would be nice to have blackframes, OOF color checkers or step wedges, clipped files, and resolution tests from various cameras at various ISOs. It gets really tiring listening to all the talk about how much noise this and that camera have, how much DR, etc, all based on certain converters.

[Bart_van_der_Wolf]

Originally Posted by Peter Ruevski

3. Take one photo at all possible ISO settings using 1/100s shutter speed (all pictures will be pitch black).

Hi Peter,

Why 1/100s shutter speed?

An unexposed shot at 1/8000s would closely approximate a read-noise only shot, while 1/100s would already accumulate 'some' thermal and amp glow noise, making it a bit harder to compare between different cameras.

I've done such a 1/8000s ISO sequence for my 1Ds Mark II, and posted the results here at OPF some time ago:


Which clearly shows the difference between the 'real' analog gain ISO sequence of 100, 200, ... , 1600, and the calculated digital intermediate (and L/H) ISO's (e.g. ISO 200 generates less noise than ISO 125 and even ISO 160).

Bart

[Peter Ruevski]

Originally Posted by Bart_van_der_Wolf

Hi Peter,

Why 1/100s shutter speed?

An unexposed shot at 1/8000s would closely approximate a read-noise only shot, while 1/100s would already accumulate 'some' thermal and amp glow noise, making it a bit harder to compare between different cameras.

You are absolutely right about 1/8000 vs. 1/100 - I would ideally like to have both, but wanted to see if someone would bother to take the exposures (not really photos ;-) in the first place.

And I am not interested in the read-out noise alone. Starting with the 1/8000 as an approximation of the read-out noise and then having a series of lets say 1/1000, 1/100, 1/10, 1, 10 seconds would be quite interesting (for you, me and John at least ;-), but that, I'm afraid, is asking too much.

For a while I have been considering writing an "engineers" review of the 30D (something like this one of the 10D vs. D70 or this one of 20D vs. 10D - but without the astronomy bias). And wanted at least some information from the MkIII because of the 14 bit ADCs - as a way of finding interesting differences - and therefore areas to concentrate the "digging" in :-)

[Peter Ruevski]

Originally Posted by John Sheehy

There really should be a repository somewhere of stuff like this. All the RAW sample sites have sharply focused images without real black; it would be nice to have blackframes, OOF color checkers or step wedges, clipped files, and resolution tests from various cameras at various ISOs. It gets really tiring listening to all the talk about how much noise this and that camera have, how much DR, etc, all based on certain converters.

Amen!
There is RAWpository but their goal is different - they concentrate solely on file format - not very useful.

[John Sheehy]

Originally Posted by Bart_van_der_Wolf

I've done such a 1/8000s ISO sequence for my 1Ds Mark II, and posted the results here at OPF some time ago:

I am curious why you have any color information for read noise.

[Bart_van_der_Wolf]

Originally Posted by John Sheehy

I am curious why you have any color information for read noise.

It's simply the result of the different ADC analog gain settings per channel. The R/G/B filtered sensels have a different gain setting to compensate for the filter densities (in addition to silicon wavelength sensitivities).

Bart

[John Sheehy]

Originally Posted by Peter Ruevski

And wanted at least some information from the MkIII because of the 14 bit ADCs - as a way of finding interesting differences - and therefore areas to concentrate the "digging" in :-)

Well, I have only seen RAWs from the 1Dmk3 at ISOs 100 and 3200 (they are not blackframes, but IRIS doesn't understand the mk3 yet, so it loads the black masked pixels as part of the image). ISO 100 has about the same pixel read noise as the 1Dmk2, when you scale the 14-bit data to 12-bit. The mk3 has a blackpoint of 1024, and a clipping point of 15280, for a usable range of 14,256 RAW levels, and a blackframe noise of 4.88 ADU. 14256/4.88 = 2921. A mk2 has a blackpoint of 128, a clipping point of 3711, for 3583 usable RAW levels, and read noise is 1.26, and 3583/1.28 = 2843, a very small difference.

log(2921/2843)/log(2) = 0.039 stops

These figures are from individual cameras, and individual cameras of the same model vary more than this. It is hard to know exactly what the real, absolute S/N is; the ratio of clipping to read noise floor is much easier to calculate, and is more relevant to DR.

I have taken the RAW data from mk3 ISO 100 images and quantized it to 12 bit, and even in the most extreme push of the shadows, I could not see any difference between the two. The two extra bits are extremely inefficient, IMO. I have quantized RAW data from numerous cameras, and my conclusion is that unless the quantization results in a read noise of less than about 1.3 ADU in the new bit depth, the quantization has no significant disadvantage, as long as you allow full precision in the conversion; IOW, if you integer-divide all RAW values by 4, multiply them by 4 afterward (zeros in the 2 LSBs), otherwise you quantize the conversion at several steps.

[John Sheehy]

Originally Posted by Bart_van_der_Wolf

It's simply the result of the different ADC analog gain settings per channel. The R/G/B filtered sensels have a different gain setting to compensate for the filter densities (in addition to silicon wavelength sensitivities).

But that depends on the actual WB used; your data seems to have a slightly different WB for different ISOs.

Wouldn't it be simpler just to measure the greyscale RAW data? I don't know what scale your green values have, if any (other than the 16x going from 12-bit to 16-bit).

[Bart_van_der_Wolf]

Originally Posted by John Sheehy

But that depends on the actual WB used; your data seems to have a slightly different WB for different ISOs.

I based my analysis on non-colorbalanced non-demosaiced Raw sensel data. In fact I subtracted 2 read-noise frames (and divided the result by sqrt(2)) to avoid non-random/systematic noise (e.g. from per sensel sensitivity/amplification differences). The results were averaged over the same 200x200=40,000 central sensels used in my other incremental exposures used to determine the analog gain per channel.

Wouldn't it be simpler just to measure the greyscale RAW data? I don't know what scale your green values have, if any (other than the 16x going from 12-bit to 16-bit).

Indeed, that is what I did, including the 12 -> 16 bit scaling to make it comparable to other cameras' 16-bit file read-outs.

Bart