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Cosmetic defects

Cosmetic defects can come in many varieties, and vary from chip to chip. Dark columns, areas where charge-transfer is inhibited unless a threshold of electrons is present, can be dealt with effectively by pre-flashing. 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 can be of great help to obtain clean images.

Other factors in addition to the required signal to noise ratio which need to be taken into account when choosing a detector are:

Wed Apr 6 22:56:39 BST 1994