Two well-corrected four-mirror telescopes

A study has been conducted of a configuration resembling that of a Cassegrain telescope with two nested mirrors in the plane of the primary and two nested mirrors in the plane of the secondary. The focal plane was located in the plane of the first and the third mirror. The four surfaces available in the device for corrections made it possible to correct for third-order spherical aberration, coma, astigmatism, and distortion.