  A complete description is given of two-mirror telescopes with a flat medial
focal surface, on which the images of stars are circles of least confusion.
Particular attention is paid to aplanats, since their field of view is
noticeably larger than that of classical systems. Two sets of appropriate
solutions correspond to Schwarzschild and Gregorian telescopes. As a result, it
becomes possible to use flat light detectors with wide-field two-mirror
telescopes. New designs are of particular interest when as few reflective
surfaces as possible are required, which is typical for space exploration and
non-optical observations.
