Previous: Flat Fields
Up: WHAT EXTRA OBSERVATIONS ARE REQUIRED?
Next: Photometric calibration
Previous Page: Flat Fields
Next Page: Photometric calibration
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.