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The third major factor in CCD performance for astronomers is saturation
level: how large a charge signal can be held by a pixel. The peak
capacity is typically 200,000 electrons, and CCDs are demonstrably linear
devices up to within a factor of two of this limit. The arrival of
further photons continues to create photoelectrons, which then tend to
spread in either direction along the column. Together with readout noise,
the saturation level defines the dynamic range of a CCD, crudely, as
(saturation-level)/(readout noise). This ratio is 200,000/50 or 4,000 for
RCA CCDs, and
40,000 for GEC CCDs, the latter corresponding to 11.5 mag.
Of course this assumes working down to the 1
level, something which
astronomers would never do. In practice, however, dynamic ranges as large
as 8 mag have been used.