Previous: Flat Fields
Next: Photometric calibration
Previous Page: Flat Fields
Next Page: Photometric calibration

Dark counts

Strictly speaking, dark count frames should be subtracted from each observation in the reduction process (section 1, Appendix 4). In practice, the dark-count is so low (Table 1) that this is rarely necessary. If it is (e.g. long exposures, very narrow-band filters, no sky counts), then dark frames must be obtained. To produce these, run procedure DARK:

Adam:> DARK 10000 (sec)

At the end of ``exposure'', the chip will be read out with data dumped to the next available run file.

To stop the run prematurely, press the break key, then

*SEND CON: (break-in)

Adam:> STOP (stop the exposure)

Adam:> READ (readout)

Adam:> DISP (display)

Adam:> KEEP (store on disk or disk + tape)

The dark count frame for the RCA chip in particular does show some structure (Fig 8), with a warm corner apparent at the readout point. Note that the DARK procedure is also a very effective way of measuring the cosmic ray rate.

Fri Jun 10 17:31:56 BST 1994