Concerning ISO:
The first question one has to ask, is to what the actual (nominal) ISO is corresponding and related. There are of course ISO norms, but those are rather thought for the consumer field and leave open a big "playing gap". Therefore, the manufacturer has to decide by himself to what this ISO should be related.
When doing a lightmetering, the result should lead to a medium grey (Lab 50/0/0) rendered as medium grey. One has to be aware here, that a RGB medium grey does not necessarily correspond to 128/128/128, respectively a centered histogram does not necessarily lead to a correct exposure.
This is strongly depending on the Gamma value of the chosen Colour Working Space: in sRGB, a RGB value of 119/119/119 correspond to a medium grey. In ECI RGB, a medium grey is given with a value of 101/101/101.
The goal of the ISO sensitivity "finding" should therefore be to reach the above value for a medium grey, with ALSO taking in count the used "contrast curve". This has lead to the value of ISO 100 as nominal sensitivity for the eMotion 75, and ISO 50 for the eMotion 54 (resp. eMotion 22), with a "default" or "standard" contrast curve of "3" in Captureshop/eXposure.
Best regards,
Thierry
Also with the ISO it's important to no forget that numbers are numbers. What some manufacturers consider ISO 800 is less than ISO 400 for other folks (I'm not talking about any specific vendor here but generally).
Boris
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