ALFOSC Bias frame, Ampl A, high gainThe vertical gradient in short exposures is typically a few ADUs. In long exposures it can be tens of ADUs, however the overscan follows the trend, hence this can be subtracted straightforwardly (see the CCD#8 pre-commissioning report).
 An average of columns 500 to 1500 of a combination of fifteen bias frames. Click here to see large image. The (trimmed) full frame median is 360.3 ADU with standard deviation of 1.34 (minimum=352., maximum=367.).
 A combined frame of fifteen bias frames. The grayscale cuts are +/- 3 ADUs. Click here to see large image. Note that the pre- and overscan regions are nearly invisible in the grayscale image.
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