A CURVATURE-COMPENSATED CORRECTOR FOR DRIFT-SCAN OBSERVATIONS

Images obtained by drift-scanning with a stationary telescope are affe cted by the declination-dependent curvature of star trails. The image displacement due to curvature and drift-rate variation increases with the angular field of view and can lead to significant loss of resoluti on with modern large-format CCD arrays. We show that these effects can be essentially eliminated by means of an optical corrector design in which individual lenses are tilted and decentered. A specific example is presented of a four-element corrector designed for the Large-Zenith Telescope. The design reduces curvature errors to less than 0.'' 074 over a 10' x 20' field of view centered at 49 degrees declination. By changing the positions and tilts of the lenses, the same design can al so be used for any field centers between 0 degrees and +/-49 degrees.