Nikon D300 Complete Manual page 284

Note: Underexposing is a bit like setting a higher ISO. Some of the
complaints I've heard from D300 users about "noisy,
unsaturated images" can be attributed to this. For example,
let's say you were shooting at ISO 200 but underexposed by
Thom Hogan's Complete Guide to the Nikon D300
ISO 3200. Still hard to see
any shift at this level, but
look closely at the detailed
area (200%) I've included
below: you should clearly
see noise in the red patch,
which is why its color is
shifting slightly.
ISO 6400 (H1.0) I hope you
can see that things took a
turn for the worse. First,
even at the larger size you
can see noise. Also note the
darker colors in many cases.
The 200% view reveals just
how bad things got.
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