An astrometric aplanatic telescope with a figurated flat secondary mirror

Abstract

In 1966 the author pointed out the theoretical possibility of an aplanatic system with a figurated flat secondary. The recent construction of a 61" astrometrical parabolic reflector with a flat secondary at the U.S. Naval Observatory, Flagstaff, Arizona, has made it possible to observe the practical performance of this type of optical systems and has induced the author to investigate the possibilities of improving still further the optics of the system.