Proceedings PaperAll-Reflecting Afocal Telescopes
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The family of afocal telescopes discussed here consists of two, three, or four confocal conic mirror sections. The two-mirror parabola/parabola combination (confocal parabolas, or Mersenne telescope) is the best known, but its performance is limited by curvature of field. The three-mirror Cassegrain/parabola combination (Offner afocal telescope) can be corrected for field curvature and is suitable for use at high magnifications. The four-mirror Cassegrain/Cassegrain combination, the least well-known design, is most effective as a unit power afocal relay. The properties of these designs will be reviewed briefly, with major emphasis given to the confocal Cassegrains design.