Exposure basics, lesson two point one (& ISO)

Started Mar 19, 2013 | Discussions thread
Jack Hogan Veteran Member • Posts: 6,944
Don't listen to me, try it for yourself - it's easy

Mjankor wrote: Can you please explain how they can be arbitrary, with respect to the ISO standard?

Hey Mjankor, SOS depends on in-camera processing. No two cameras process an image the same way, in fact there are very large variations, even from mode to mode within the same camera. But don't take my word for it, check it out yourself. Set your camera to a Neutral mode (say Portrait), meter off a uniform wall and take a shot. What value does the wall show in sRGB?

Now change the camera mode to Landscape, meter off the same wall and take a second shot.
What value is the wall now in sRGB? Is it 118? is it the same?

Try both scenarios with your other camera. How consistent are the four figures?

Can you also please tell us what DPR are doing, when they do their ISO tests to the 12232 standard?

"If you want to compare ISOs between cameras from our reviews, look at the ISO test section (on the Noise and Noise Reduction page). This is where controlled test results are reported, essentially using the SOS method of ISO 12232:2006. The rest of the testing is based on knowing this SOS ISO calibration, as all test scenes have specific grey patches that are white-balanced and exposed as closely to L=50 as possible (i.e. within 1/6 stop)." - Andy Westlake

I am not an expert on DPR testing procedures, so I am not the right person to ask. But the first question that comes to mind is 'Do cameras set up as above capture a consistent tonal range, or merely present output images of the same average brightness/contrast' for a given exposure?

And, finally, can you please tell us how every camera I've looked at is consistent in this test? Why do all the cameras agree, if it's an arbitrary standard (oxymoron, I know)?

I assume this is an experiment you've done. Please tell us your results and methodology.

I am starting to get the impression that you are not genuinely interested in my answers but that your questions have an agenda behing them, and that you are never going to be satisfied with any answer I give unless itìs what you want to hear. My opinions have been made clear. Perhaps now you can ask other knowledgrable contributors like bobn2 what they think. Or report back with your findings for the exercise above and answer your own question.



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