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Orientation of the chip

Alignment of the CCD is such that the long axis of the detector corresponds to the long axis of the TV although the TV scan causes the RA axis to be slightly tilted to the long axis of the chip. This position corresponds to E-W on the sky and to a Cassegrain rotator position of 359.2 degrees. The TV should be parfocal with the CCD and the autoguider although when the telescope is refocussed the TV will be slightly out of focus. Figure 3 shows the views which are obtained if the Lexidata display is set up so that the CCD frame origin (x=0, y=0) is located at the lower left-hand corner. The long axis of the chip is arranged so that it corresponds to the long axis of the TV. The TV scan switches must be H (up) and V (down). The Cassegrain rotator should read 0.

When the grisms are being used the directly-viewed object should be centred 60 arc seconds west of the chip centre. The dispersion direction is also along the long axis of the chip.