Comparison of on-axis three-mirror-anastigmat telescopes

Abstract

We compare and contrast the Korsch (1972) full-field three-mirror anastigmat telescope (TMA) to the Korsch (1977) annular-field TMA. Both TMAs offer flat fields with comparably good aberration correction and comparably good telephoto advantage. Both offer good accessibility of the focal plane. The advantages of the FFTMA are its extremely uniform focal length over its field, its nearly telecentric final focus, and the fact that there is no hole in the center of its field. The advantages of the AFTMA are its complete accessible cold stop (essential if a warm telescope is to be used to image the sky at near-IR wavelengths) and its low sensitivity to mirror location error. Either alternative can deliver diffraction-limited visible-wavelength images over a one degree diameter field with a two meter aperture.