@bigblue1ca. Well I asked the same question some years back of Chuck Westfall (Canon) and he supplied me with the Standard Specification "Sensitivity of Digital Cameras CIPA DC-004 (2004)". I would be happy to send it to you (400K PDF) as a PM, but I don't think its possible, any ideas?
Last edited by Raid; 02-16-2012 at 02:59 AM. Reason: syntax
Canon EOS 7D, EF-S 10-22, EF 24-105L, EF 50 f1.2L, EF 70-300L, 430EX.
"Criticism is something you can easily avoid, by saying nothing, doing nothing and being nothing." - Tara Moss
Interesting all, thanks. Raid, sure that would be great, you could just add @gmail.com to my username and email to me if that works for you.
Or, you could click HERE for the pdf.Originally Posted by bigblue1ca
As for, 'how does Canon know that ISO 102400 is one stop more than ISO 51200', put in lay terms, it's simple math. The sensor detects photons of light, each pixel 'counts' those photons for the selected exposure time, storing them as electrical charge. If the ISO is set to 100 (let's assume that's the 'base' - any sensor has only one base ISO), that amount of charge is converted to a digital signal of a certain numerical value, which is the value assigned to that pixel for brightness (the position under the RGB mask determines the color that's assigned). If the ISO is higher than 100, up to the top 'native' ISO (i.e. non the expanded 'H' or 'L' settings), the sensor applies an analog gain to the signal prior to converting it to digital. Analog gain is like 'turning up the volume' on the signal electrically, and the amplifiers are precise, unlike turning the know on your stereo, it can apply a 2-fold amplification for ISO 200, a 16-fold for ISO 800, etc. If you've selected an expanded ISO like ISO 102400 on the 1D X, that is a digital gain applied after the analog signal has been converted to digital. So for the ISO 102400 case, the camera is applying the maximum analog gain (to get to ISO 51200), then it just takes the numerical value assigned and doubles it to reach ISO 102400.
Thanks Neuro that makes sense.
There is enough leeway in the "standard" that manufacturers can pretty much make up whatever they want for the "ISO" -- and they do. The ISO standard did include a simple and obvious method that everyone should use, but no one does. Too bad, because it would have been nice to be able to go from one camera to the next without having to spend the time figuring out what the iso setting *really* means. Many manufacturers, like Canon, aren't even consistent across model lines in the same generation, let alone different generations and different manufacturers.
Is that true for all cameras? I thought Canon defined 'native' ISOs as analog gain and 'expanded' ISO as digital gain ("pushing the RAW").
It was true for all cameras until a few years ago.
Not really. There is a strong correlation between native ISO and analog gain, but there are several exceptions. For example, on the 5D2, 6400 is a 'native' ISO, but it is based on digital gain (3200 is the highest analog-only gain).
Personally, it doesn't really matter what the highest analog gain is -- I'm more interested in the highest *useful* analog gain. For example, the D7000 has analog gain up to ISO 1600, but going above ISO 200 in raw has only downsides -- no benefits. (Same with going above 1600 on the 5D2 -- although there is a slight reduction in pattern noise, for me it's not usually worth the loss in highlight headroom.)
Really? I was told 1600 was the highest.
If 3200 is the highest analog-only gain, then what do you mean when you say 6400 is 'native'? Do you simply mean it is not an expanded iso?
Yes, that's what I meant.
I don't know for sure that 1600 is the highest real iso on all of them, but a friend who has examined raw files for more than one canon camera (including the 5DII) tells me that for those he has looked at, everything above 1600 is achieved by pushing the raw. Thus it is definitely not the case that pushing the raw only happens with "expanded" iso settings.
Last edited by Jon Ruyle; 02-17-2012 at 04:21 PM.
Posting Permissions
Reply With Quote