PNS MANUAL: Taking dome flats

Taking dome flats

There is an incandescent lamp in the WHT dome for dome flats. We found that pointing the telescope at 45 degrees elevation at a blank bit of the dome, and illuminating this from below with the lamp, gave rather uniform illumination, certainly sufficient for measuring the pixel-to-pixel variations in the flat field. As the shutter is rather slow, the exposure times have to be controlled by swithing the lamps on and off while the shutter is fully open, then closing the shutter, and reading out. This requires a fit person, a lazy person, and two synchronized watches. The procedure is as follows. It assumes a 20-sec integration time.
  1. Make sure CCD readout parameters are OK (window, readout speed).
  2. Set up the dome flat lamp as described above, and switch it off
  3. Lazy person sits in front of controls. Energetic person put on sneakers. Both synchronize watches and agree on lamp switchon time (1 minute into the future is OK).
  4. Energetic person goes to lamp in dome.
  5. A little (< 20 sec) before agreed time, lazy person issues expose 60 "Dome flat" on DAS, and expose 60 on PNS PC.
  6. At agreed time, energetic person switches on dome lamp, for a total of 20 secs, then switches it off again.
  7. Repeat from step 2 as often as desired.
If walky-talkies are available a less energetic approach is possible!
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