Digital has small dynamic range
and to handle high dynamic range subject, one must stack
several shots. It is not only that digital has high dynamic range; in fact, “dynamic range” (at a particular ISO
number) is not even a number but is a
curve (or two) which describe how dynamic range depends on the
level of resolution you want to keep. These curves also describe
the “color” of noise (“what kinds of patterns are made by the noise”). We provide 6 numbers which
describe these curves.
So: if one is ready to sacrifice some details, the range may be
VERY high (20 steps or somesuch)!
Magnification of a loupe is 250/f (it turns out that the newer
WikiPedia already has a correct formula).