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Each arm has a slide for an optional cross-dispersing grism, although at present only the blue cross-disperser has been purchased. The cross-disperser is a special ruling 100 lines/mm fused silica grism blazed at 4400 Å. This will be used in conjunction prime disperser which is a Bausch and Lomb 75 lines/mm grating blazed at 3 microns, to provide complete spectral coverage from 3000 - 5600 Å on an EEV P88300 or Tek 1024 CCD or the IPCS on the blue camera. The cross-dispersed mode will use orders 5 to 10, and the maximum slit length to avoid order overlap will be 30 arcsec. The spectral resolving power of the cross-dispersed mode is about 2200. Figure 7 shows the format of the cross-dispersed spectrum superimposed on the outlines of the IPCS and a TEK 1024 CCD.
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