DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
Martin.au Forum Pro • Posts: 13,259
Re: Well now, that was fast

Jack Hogan wrote:

texinwien wrote:

I see you've completely abandoned your first example - the one I took apart, piece by piece. The one where you forgot to equalize exposure (sort of embarrassing, eh).

I also see that rather than respond and admit that your example was flawed, you've now turned to fictional 'examples' that contain no pesky variables for you to keep straight - exposure, etc.

That must be some kind of record - I've never seen someone drop one invalid 'proof' and switch to a completely fictional one in such a short span of time. Bravo.


Ciao Jackie - get back to us once you put together a real-world example that illustrates your argument... Or else, once you realize that that's a fool's errand, and are ready to admit that you were wrong. We're waiting here with open arms.

So many words in vain, texinwein You've obviously not read my posts through so let me summarize them here. I have addressed two and only two main issues over several posts:

1) In-camera ISO labelling is inconsistent from camera to camera and from manufacturer to manufacturer
2) Given the problem in 1), how does one then go about comparing two cameras fairly, with the same scene and the same photographic intent?

1) is a self-evident fact. The answer to 2) is also simple:

Same scene, same lens, same shutter speed, same f/number, same tonal range (highlights and shadows) recorded. The first four are self-explanatory. To capture the same tonal range you could simply read the ISO difference in stops off of the DxO graphs, or you could figure it out yourself like this:

set the two cameras up manually to have the same ss and f/n for the same scene. Then take a capture of a gray card with both at the same nominal ISO, say 1600, and correct the ISO of one of the two while keeping Exposure fixed iteratively until the gray card appears in the same spot of the Raw histogram of both*, say 10% of full scale. This way both cameras will be recording the same range of incoming tones, from shadows to highlights. Having set them up to respond equally to the incoming light, you can now take a capture of the scene, ensure with your Raw converter of choice that the brightness of the output images are comparable and judge their relative IQ - SNR in this case - fairly, apples to apples.

If you were to go through this exercise with the EM5 and the G3, you'd find that you'd end up with the EM5 at in-camera ISO 3200 and the G3 at 1600, the same Exposure and very similar SNR (EM5 slightly better as per DxO graph). I am not suggesting that you'd want to shoot evey scene in the field like that, but that if you wanted to compare the two cameras fairly that's how you'd need to do it. On the other hand, comparing two cameras at the same ss, f/n and in-camera ISO setting is more often than not meaningless because of 1)

Is what I am saying clearer now?

* Great free program to obtain the Raw histogram is RawDigger

I contest point 1). Citations or examples please. A stop or more please.

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