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It is possible to change rapidly from long slit spectroscopy to imaging at the Cassegrain focus by inserting a diagonal flat into the light path in the A&G unit, sending the light to a CCD camera mounted at the auxiliary port. At this f/11 Cassegrain focus, the telescope scale is 4.51 arcsec/mm at the detector, which gives a scale of 0.10 arcsecs per 22 microns CCD pixel. At present GEC P8603, EEV P88300 and Tek 1024 square CCDs are offered at the Auxiliary focus; these detectors are described in more detail in Chapter 2. Table 1 summarises the pixel and field sizes given by these CCDs.
The unvignetted field at the Auxiliary port is currently limited by the shutter to 2.0 arcmin diameter, thus the final unvignetted field is the intersection of this circle with the rectangle given in the table.