The Spartan Infrared Camera provides tip-tilt corrected imaging for the SOAR Telescope in the 1-2.5μm spectral range with four 2048x2048 HAWAII2 detectors. The median image size is expected to be less than 0.25 arcsec (FWHM), and in the H and K bands a significant amount of the light is expected to be in a core having the diffraction-limited width. The camera has two plate scales: 0.04 arcsec/pixel (f/21) for diffraction-limited sampling in the H and K bands and 0.07 arcsec/pixel (f/12) to cover a 5×5 arcmin2 field, over which tip-tilt correction is substantial. Except for CaF2 field-flattening lenses, the optics is all reflective to achieve the large field size and achromaticity, and all aluminum to match thermally the aluminum cryogenic-optical box in which the optics mount. The Strehl ratio of the camera itself is 0.95-1.00 for the f/21 channel. The optics (including the off-axis aspherical mirrors) will be aligned with precise metrology rather than adjusted using interferometry.
The entrance of a cryogenic instrument is often a major heat load, since the opening in the cold instrument has a large solid angle. We present a novel thermal reflector that, placed between two openings, reduces the load by reflecting radiation emitted in the hot opening and not directed toward the cold opening. In the Spartan IR Camera, this thermal reflector, placed between the vacuum window and the field stop, reduces the load by a factor of 2.5, which is 1.5 times the limit defined by the size of the field stop, the minimum window size, and the separation between the two.