Acquisition and Guiding at Prime

  This is mainly used with the prime focus CCD camera. The A&G unit is mounted on a rotator which allows the detector to be rotated to any position, although it is normally operated at one of the cardinal points. The default orientation is 180 degrees.

• Acquisition. No direct viewing of the field is available for the prime focus. The telescope points sufficiently accurately that any object with a reasonably accurate position can be acquired close to the centre of the CCD detector. This can be verified using a short CCD exposure.
• Autoguider. The prime focus autoguider is identical to that at Cassegrain. The detector is an FW-130 image dissector with an S-20 photocathode. There is a single filter, at present a broad-band green filter. Ideally guide stars should be selected in advance of the observing run, using Figure which shows the area of sky within which guide stars may be selected.

  Alternatively they may be selected from the finder telescope and then acquired by scanning a 2.52.5 area around the selected position. Stars with magnitudes in the range 714 will probably be suitable. There is an overlay of the TV image which shows the area from which guide stars can be chosen. To get this overlay the TV camera must be on when we start ADAM. By default the system displays the Cassegrain overlay.

• Important At prime focus you must select the guide star before you start the exposure.