The Cerro Tololo Infrared Imager (CIRIM)
uses a 256 
256 HgCdTe NICMOS 3 array from the Rockwell
Science Center. The array is operated by the WILDFIRE array
controller system built at Kitt Peak. A liquid nitrogen cryostat
contains the imager optics and the detector, which is cooled to 77K
using a combination of liquid nitrogen and a
closed cycle cooler. The optical design of CIRIM is a three
element focal reducer, which generates a well-focused pupil image and
a demagnification of the telescope plate scale of 1.5. CIRIM contains
three filter wheels and a selection of Lyot stops.
CIRIM can be operated at the f/14 and f/8 foci of the CTIO 4-m and 1.5-m telescopes. In principle, CIRIM can also be operated at f/30 and f/10 (1m), but these modes are no longer supported. At a given telescope the plate scale is set by selecting the f/ratio. The choice of f/ratio should be arranged prior to your observing run. At the 1.5m telescope a ``flip'' is possible between f/13.5 and f/8 (in about 20 minutes). If you plan to change f/ratios during an observing run please consult with observer support or your staff contact well in advance. The scales for the these telescopes are given below;
Note that there is some lateral chromatic aberration in the imager, so scales are slightly different at different wavelengths. The effect is small and will not be apparent for most programs, but anyone looking for color gradients in extended sources should plan to correct for this effect.