The center-field camera is used only in the single slit operating mode, and images a 30 arc-sec field of view at 0.20 arc-sec/pixel. The center-field camera, when inserted into the optical path, vignettes the focal surface. For this reason, the camera is fully retractable, to avoid vignetting when not in use. A pick-off mirror is used to sample center field, and reflects the beam into the camera optics.
A turret assembly allows an alternate set of optics to be swung into
position. When used in conjunction with a second fixed position,
slightly removed from the optical axis, this downward looking mirror
views reflection at 
5 degree angle off the polished surfaces of
the long slits. The field of view of this camera is approximately
30 arc-sec, but at the same 0.20 arc-sec/pix scale. In addition to the
retracted, center field, and slit viewing positions (y-motion), the
camera can be scanned along the slit (x-motion) to allow acquisitions
of objects one field diameter off of the telescope optical axis.
As with the principal guider, an infrared filter will be provided for work during fuller phases of the moon. As with the principal guider, the focus will be fixed with respect to the focal plane.