I didn't understand about ISO. I am familiar with film speed ratings and
the tradeoffs between speed and grain size. Are you saying that each
camera has an ISO speed rating like that of film? And that the tradeoffs
are comparable to those of film? How does the lens size (focal ratio or
objective lens diameter) figure into that? Does a lens with a small focal
ratio enable a camera with a high ISO speed to take better-quality images
under low-light conditions? So that, if low-light quality takes precedence
over camera size, you want the smallest focal ratio (largest lens) and
highest ISO? Or will a more moderate ISO give better quality under the
same light conditions? That is, if a small lens and high ISO is adequate
for the light, a large lens and moderate ISO will give a better image in that
same light?

-- Jeff, in Minneapolis

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