In message .com,
" wrote:

RichA wrote:

Some reviewers criticize the Nikon's for not having a
100 ISO setting, they start at 200. This is supposedly
because Nikon sensors in the cameras that feature this
are more sensitive so that a Nikon at f4 and 1/250 of a
second has an ISO of 200 while another camera will be at
100. Is this true? IF so, there should be less noise and
more dynamic range in the Nikon set at 200 ISO than another
DSLR set at 200 ISO.

ISO is constant*standard_effect/necessary_exposure, and this is
directly tied to the signal-to-noise ratio.

Funny; my 10D has lower RAW values with the same subject, lens,
aperture, and shutter speed than my 20D, and has a bell-curve of noise
3x as wide at "ISO 800", giving a S/N ratio about 4x as high for the 20D
at the same ISO. ISO 100 has a slightly narrower bell-curve of noise on
the 10D.
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John P Sheehy