In normal operation, slit viewing is accomplished by means of a TV mounted on the instrument rotator. Two positions of the instrument rotator mirror carriage provide for direct viewing of the field, for target acquisition and for viewing light reflected from the spectrograph slit. The TV camera provides for both wide field viewing for target acquisition, and the viewing of light reflected from the slit jaws.
Field of view approx. 2.5' by 2'. Cannot see slit. Used for field identification and rough centering. The telescope operator then switches to slit viewing mode to center object in slit.
Field of view approx. 50" by 35". It is in this mode one takes data.
Auto guiding is normally accomplished using a separate TV camera, optically coupled to the offset guide probe, mounted in the instrument rotator, in conjunction with a leaky guider module. The guider probe can access many arcminutes of field and the system can guide on stars down to around 16th magnitude.