  Two all-spherical catadioptric optical systems with a Mangin mirror are
described. The design A (aperture 500 mm, f/2.0) has flat field of view of 7
deg in diameter; the design B (aperture 1000 mm, f/1.7) has 10-deg flat field.
Both designs show near-diffraction-limited images. The D_80 diameter for the
design A in the integral waveband 0.45-0.85 mcm varies from 1''.3 on the
optical axis up to 2''.2 at the edge of the field (6.2-10.7 mcm); the
corresponding range of the D_80 diameter for the design B is 1''.5-1''.9
(12.4-16.2 mcm). The designs include simple glass types, mainly Schott N-BK7
and fused silica. In case of need, better images could be attained by a choice
of other glass, aspherisation of some surfaces, etc.
