A dedicated A&G unit is available for observations at f/15 with the CCD camera. This is described in more detail in the ``JKT CCD Users Guide'' (La Palma User manual no. XVIII). Figure is a diagram of the A&G unit.
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Figure: The
acquisition and guider unit used with the CCD camera
at the f/15 Cassegrain focus of the JKT, showing grisms,
filters, shutter assembly, TV camera, autoguider, drift-
scan table and CCD cryostat.
The facilities provided are:
Guide stars can be found most efficiently using the Guide-Star Server (GSS), see section . Alternatively, they can be acquired by offsetting the telescope so that the field is viewed (in sections) by the acquisition TV camera. There is an automatic procedure to perform the search.
The autoguider has two sets of filters: ND and colour. For the highest accuracy at large zenith distances, the colour filter should be similar to that of the CCD camera. This minimises the effects of atmospheric differential refraction.
It is important to note that the autoguider cannot be focussed independently, so the total physical thickness of the filters in front of the autoguider must match that of the CCD filter in use. This presents no difficulty for the standard La Palma filters, but observers bringing their own filters should check the ``JKT CCD Users Guide'' (La Palma User Manual XVIII), where a list of the available autoguider filters is given, together with their thicknesses.