Why bother changing base ISO?

Started Jul 18, 2007 | Discussions thread
OP Jim Kaye Senior Member • Posts: 2,794
Re: Posterization

According to Hans's analysis, underexposure by 4 stops (ISO 1600 vs
100) would result in only 8 bits of data (256 tones). That is what
you get with a JPEG, but in the case of the underexposure, the gamma
is 1.0. Converting to a gamma of 2.2 would result in only 184 tones
(see Bruce Lindbloom's levels calculator).

Also, for the D200, read noise is higher at ISO 100 (10 electrons) as
compared to ISO 1600 (7.4 electrons). See Roger Clark's analysis:


According to Roger's analysis of unity gain, with the D200 there is
little benefit in setting the ISO higher than 800.

OK, Bill, but I guess that means there is a measurable benefit in setting the ISO appropriately within the range 100-800 (as opposed to bumping the exposure setting in post). Maybe you know of some comparison images someone has posted that show the difference clearly?
Jim Kaye

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