Moose's illustration was very nice indeed and totally applicable here but not
for all situations. Some of the Sony sensors become "ISO invariant" at fairly
low ISOs" likely due to quite low apparent read noise
and enough bits in the RAW file. More pattern noise explanation though hard to
beat Moose's illustration here.:
http://www.clarkvision.com/reviews/how-to-interpret-reviews/
Curiously Nykon clips the Raw data making noise appear lower and DR higher if
not taken into account--Implications for astrophotog. To quote Roger Clark:
"Clipping of the raw data will skew measurements of the read noise and dynamic
range if the clipping is not accounted for properly. In the case of the Nikon
D800 at ISO 100, the clipping of data reduced the measured read noise by almost
a factor of 4 (2 stops) and that made a corresponding increase in dynamic range
of 2 stops if clipping is not accounted for. Reviews that do not account for
this will derive parameters and scores that make the camera look much better
than it really is. Perceptually, the clipping the way Nikon implements it still
produces amazing images and in many photographic situations, photographers will
not be hampered by this clipping issue. But clipping could limit detection of
faint signals if images that have clipped lows were co-added (which is commonly
done in astrophotography), because averaging clipped data still results in
clipped data. It is important to know if the camera you might purchase might
limit your intended photographic applications because of
clipped data, or if you have the camera, how you might work around such a
problem. "
More noise about noise, Mike
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