Check dome flats

Observers should examine at least one dome flat of each filter to make sure they have no obvious flaws. Correct dome flats will have

  • Count levels roughly as follows. These are net counts, i.e. difference between array pixels and overscan pixels.
Filter Exposure time ADU
u 30s ??
g 15s 14k
r 20s* 17k
i 22s 17k
z 10s 17k
Y 10s 21k

(*) note that the dome flat scripts take r-band exposures at two different exposure times to check linearity.

  • All 62 science CCDs have read out properly
  • All CCDs (except #61=N30) are uniform to a few percent
  • No visible interference patterns or striping (a pattern of concentric rings is normal, as are bright strips along the CCD edges).