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Cosmetic defects


Cosmetic defects can come in many varieties, and vary from chip to chip. Dark pixels, as a result of local poor charge-transfer inefficiency (traps) are unavoidable, but for most of our grade-1 chips only a small number (<10) should be seen, and then only at low signal levels. Defective areas such as bad columns, bad pixels or hot pixels cannot be cured. Each chip has its ``fingerprint'' of cosmetic defects and care should be taken to avoid the worst affected areas when positioning an object on the chip. Multiple exposures in which the object of interest is shifted to a different location on the chip between exposures may help to obtain clean images.

Tue Aug 15 16:42:46 BST 1995