PNS MANUAL: Taking Twilight Exposures

Twilight sky exposures are best taken as if they were science exposures, i.e. controlling the exposure duration with the shutter even though it is a little slow. The alternative, of leaving the shutter open and reading out the CCD introduces far greater nonuniformities as the readout takes longer than the shutter motions.

So twilight sky exposures should be taken in the same manner as regular science exposures.

Sky flats are now handled by the DAS script with the alias "skys"; like "expose" this allows time for the PNS shutter to open and close but gives the images the correct OBSTYPE.

  1. At the DAS enter skys t "SKY"
  2. After the CCDs start integrating, at the PC enter expose t
where t is exposure time.
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