Achieving a wide-field near-infrared camera for the Calar Alto 3.5-m telescope

The ongoing development of large IR array detectors has enabled wide field, deep surveys to be undertaken. There are, however, a number of challenges in building an IR instrument which has both excellent optical quality and high sensitivity over a wide field. We discuss these problems in the context of building a wide field imaging camera for the 3.5m telescope at Calar Alto with the new 2K by 2K HgCdTe HAWAII-2 focal plane array. Our final design is a prime focus camera with a 15 feet field-of-view, called Omega 2000. To achieve excellent optical quality over the whole field, we have had to dispense with the reimaging optics and cold Lyot stop. We show that creative baffling schemes, including the use of undersized baffles, can compensate for the lost K band sensitivity. A moving baffle will be employed in Ogema 2000 to allow full transmission in the non-thermal J and H bands.