Two-mirror/three-surface system for large optical astronomical telescopes

In this paper a new optical system for large astronomical telescopes is proposed. The center part of the primary mirror of a Cassegrain or R-C system is utilized to build a third mirror. Should we exchange the secondary of a Cassegrain or R-C system with another second mirror, the optical system becomes a powerful three-mirror system with good image quality and a relatively wide field. General equations for eliminating spherical aberration, coma, and astigmatism are given. An example of a 2-meter telescope system of this type is calculated and optimized.