The Ritchey-Chretien Reflecting Telescope

Abstract

THE reflecting telescope possesses one obvious advantage over the refractor, in that the position of the focus is independent of the colour of the light used. But as an offset to this all types of reflectors which have been used by astronomers suffer from the fact that the field of good definition is comparatively small. It is true that, provided the mirrors be correctly figured, rays of light parallel to the principal axis of a Newtonian or Cassegrain reflector converge accurately to a focus, but a beam of parallel rays coming in in any other direction does not do this, and appreciable coma sets in at a comparatively small distance from the centre of the field of view.