Three wide-field telescopes with spherical primary mirrors

This paper presents three optical designs based on the work of Maurice Paul. Paul's three-mirror anastigmats produce well-corrected, distortion-free fields of view. His design equations can be solved for a spherical primary mirror with one limitation: the image field is curved. Adding all-spherical refractive field-flattening optics yields well-corrected, flat image-fields of two degrees angular diameter or more. These designs can be scaled to very large telescopes with current technology.