CCDs have revolutionized astronomical imaging. With earlier photographic plate
technology one had a different detector for every exposure. Because the same
CCD detector is used for all exposures, it is possible to correct for its
defects with one set of calibrations. By combining many of these corrected
CCD exposures it is then possible to image far fainter objects. Another CCD
advantage is its huge dynamic range in the stored image: from ten electrons
to as much as 200,000 electrons per pixel.