A catadioptric telescope with a cassegrainian layout. Between the secondary and the image plane a two-element, zero power lens is located. In all cases a spherical secondary is used. The only aspheric surface is the primary mirror.
The corrector is a BK7 double meniscus lens with pairwise equal surfaces - should mean easier fabrication and testing of surfaces since they can be grinded and tested against each other.
Here are some example designs with a primary mirror diameter of 200 mm. All lengths are in millimeter.
Visual flat field cassegrain at f/9.9
Elliptical primary. 25% optical obstruction. (A slightly better design is obtained if increasing obstruction to 30%. OSLO file here)
Photographic flat field camera at f/3.7
Primary and secondary has same curvature. Hyperbolic primary.
Photographic flat field camera at f/5.5
Primary and secondary has same curvature. The design is with a parabolic primary. (A slightly better design is obtained with a hyperbolic primary. OSLO file here)
Comments and questions are welcome! Mauritz Andersson