Omega Prime: The wide-field near-infrared camera for the 3.5 m telescope of the Calar Alto Observatory.

Omega Prime is a wide-field near-infrared camera for the prime focus of the Calar Alto 3.5 m telescope in Spain. The detector is a 1024 x 1024 pixel HAWAII array made by Rockwell. The image scale is 0.4 arcsec/pixel, giving a field of view of 6.8 x 6.8 arcmin. In order to maximize the throughput, the optics were designed as a prime focus corrector with only three lenses. This simple design without a cold pupil provides an excellent image quality over the entire field of view. To reduce thermal background at wavelengths longer than 2.2 mu m, Omega Prime has a series of cold internal baffles and an additional toroidal mirror outside the dewar. This annular reflector causes detector pixels to "see" mostly the cold interior of the camera. The camera has been in operation since May 1996 and has been used for a variety of scientific programs, including a very deep K' survey covering 1000 square arcmin to a 5 sigma limit for point-sources of 20.5 magnitude.