Nikon D300 Complete Manual page 69

V1.02
dynamic range (some others measure a bit differently and
come up with a slightly different number; we'll get to that in a
moment). Using the same system for the slide film I use
(Provia F), I can capture about six stops of range. With the
negative film I use (Portra) I usually measure eight or nine
stops (processing and printing can have an impact).
The camera dynamic range of the D300 is fixed, but the
situations you'll encounter and wish to photograph aren't
fixed in their scene dynamic range. Sometimes you'll find
scenes that have very little range in exposure (said to be low
in contrast), sometimes you'll encounter situations that have
extreme variations in exposure range (said to be high
contrast).
In terms of our sensor and the buckets in which it collects
light (photosites), camera dynamic range is restricted at each
end by different things. At the bright end, as I've alluded to
before, the bucket has a limit to what it can hold. Once the
bucket is full, it doesn't matter how many more light photons
strike it, they won't be collected, and thus not measured.
At the other extreme, we also have an inability to measure
small amounts of light. Imagine it this way: let's say you just
washed your bucket and gave it a quick wipe to dry it. Now
one drop of rain hits the bottom of the bucket. Can you
measure how much rain has fallen? Well, no. There's residual
moisture in the bucket from the cleaning, and we haven't
collected enough new water to distinguish that from the
residual moisture. Likewise, with sensors: there are residual
electrons in and around the photosite and we need to convert
enough light photons into electrons so that we can
differentiate the two.
Technically, engineers measure camera dynamic range as the
difference between the full bucket (electron well capacity of
the photosite) and the measurable empty bucket (the
minimum data that can be read, which equates to the
baseline of underlying noise, sometimes called dark current
Thom Hogan's Complete Guide to the Nikon D300 Page 69