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The detector should be mounted on LDSS-2 and set to the correct back focal distance and orientation by technical/support staff. The detector position and orientation is determined with the aid of three micrometer heads which measure the distance between reference surfaces attached to LDSS-2 and the detector. A fourth micrometer head measures the rotation about the optical axis. This set of four micrometer readings uniquely defines the correct position of the detector. Thus, once these numbers have been determined, it should be possible to reposition each detector correctly without having to redetermine the correct position using optical tests each time it is interfaced to LDSS-2. However, in practice it is necessary to check that the positioning is correct every time a detector is interfaced to LDSS-2.
The optical system and detector must be aligned so that
To check the alignments, direct images of the focus mask illuminated by the Tungsten calibration lamp are analysed using routines on the DMS. When satisfied with these adjustments, the best focus must be determined for both spectroscopic observations and for direct imaging. For spectroscopy the focus must be chosen to give the best compromise over the full spectral range required. For photometry the focus should be optimized to give the best images for a particular filter.
The optimum order to do these tests is as follows:
The following sections deal with the determination of rotation, tilt and focus in more detail.