Algorithm for calculating anastigmatic three-mirror telescopes. II. Spherical primary mirror case

A version of the general algorithm (Terebizh 2019; 2020) for calculating anastigmatic three-mirror telescopes is presented, assuming a spherical shape of the primary mirror. This case is of particular interest in connection with the creation of large telescopes. The input parameters are the natural characteristics of the telescope: equivalent focal length and relative diameters of mirrors; the result is a wide field of view design with all conic surfaces, free of the four major third-order aberrations. The ranges of values of input parameters in which acceptable solutions exist are clarified, and examples of optical systems of two main types are given. The sphericity condition of the primary mirror imposes strict requirements for the rest of the characteristics of three-mirror anastigmats, which significantly narrows the class of practically attractive systems.