LARGE APERTURE CATA-DIOPTRIC ASTRONOMICAL TELESCOPE WITH CORRECTED COMATIC ABERRATION OF PARABOLIC REFLECTION MIRROR

摘要

PURPOSE:To expand the angle of view with the corrected comatic aberration of a parabolic reflection mirror and to increase an aperture ratio with the reduced focal length of said mirror by disposing a scale-down lens system near the image plane of the parabolic reflection mirror provided in the main barrel of a telescope. CONSTITUTION:A lens group 4 of the two-element constitution consisting of a convex lens G1 having a biconvex face and a concave lens G2 having a biconcave face is disposed on the outside of a main barrel of a telescope. The luminous flux focused by a parabolic reflection mirror 1 mounted in the barrel 2 is drawn to the outside of the barrel 2 by a plane reflection mirror 3 disposed at 45 deg. inclination, whereafter the luminous flux is further focused by a scale down lens system 4, and arrives at an imaging plane 5. The comatic aberration which is the most significant defect with the mirror 1 is corrected by said lens system 4 without spoiling the advantage, i.e., zero spherical and chromatic aberrations, of the mirror 1, whereby the focal length of the mirror 1 is reduced by about 20% and the aperture ratio of the entire optical system is increased.