A FAST FOCAL-REDUCING CAMERA FOR CCD IMAGING

This paper describes the design and performance of the OREAD focal-reducing camera, constructed for use at the Cassegrain focus of the Michigan-Dartmouth-MIT Observatory McGraw-Hill 1.3-meter telescope. OREAD is an all-refractive optical system providing a 50-mm collimated beam suitable for commerically available narrow-band filters or grisms. Its collimator and field lens are custom-made to decrease the severe coma which would otherwise be present at the extremities of its 30-arc-min field. When used with a CCD such as the TI 800 x 800, OREAD provides a field of view of 0.1 square degree at 1."5 pixel-1. The focal ratio of OREAD of f/1.63 allows sky-limited narrow-band images to be obtained with exposures of only moderate duration. In an Appendix we examine some limitations inherent in coarsely sampled data obtained with CCDs.