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Acquisition

Select a suitable rotator PA, using

Adam:> ROTPOS < PA in degrees> (standard value 180)

bearing in mind the existence of guide stars (see below), the fact that displays are in a comprehensible orientation if the rotation is at 0, 90, 180 or 270 and the possibility of losing liquid nitrogen if operating at large zenith distances in the North with PA significantly different from 180. The overlay on the finder display changes position automatically. Relative locations of the CCD chip and guide-star acquisition field are shown in Fig 1.11. The pointing of the INT is quite good enough (< 5 arcsec rms) to ensure that your object will be in the middle of the chip (if its position is accurate, of course). If you have any doubts, and to check the exposure time, do a GLANCE. When estimating exposure times (in particular, the time to saturation) do not forget to subtract the bias level.

Autoguiding is essential for exposures longer than 300s and is recommended for any longer than 100s.