In this mode the acquisition/comparison arc mirror system is withdrawn and the Cassegrain image formed directly on the spectrograph slit. The polished slit jaws are inclined with their normal 7.5from the telescope axis so that the reflected beam has an axis inclined at 15to the telescope axis. The slit viewing mirror enables the TV camera to view the reflected image. The slit can also be viewed via an eyepiece substituted for the TV camera. In practice the TV system is used because of its efficiency and convenience.