To that end, we have instigated a systematic program of standard CCD tests at ESO, La Silla. We currently test one CCD each week, and thus each CCD is tested every 3 months. We can then investigate any problems that we identify with more sophisticated methods, or, if we judge the CCD to be functioning satisfactorily, the test results provide a baseline of its performance. All images include bias overscan regions in both dimensions, cover the entire light-sensitive, unbinned area of the CCD and are collected under the same circumstances as normal observing. The light source used to obtain the flat fields may be either an LED or a beta light.
Beta lights consist of a fluorescent screen stimulated by decay from a small bulb of tritium.
Two 16-point linearity curves. In this way, we can reject trends observed in the CCD response that are probably caused by the effect of temperature variations on the light source. The ordinate is the variance of the same region in the image that results from the difference of two images of the same mean counts. The straight lines are linear fit to the data. The exposure times have been corrected for a shutter delay of 1.4 seconds.