A general algebraic theory based on first and third order equations has been developed for systems composed of two separated spherical mirrors. The name inverse cassegrainian systems has been provisionally assigned by the author to this general arrangement. One subgroup is the aplanatic Schwarzschild mirror system. The theory not only includes previously known examples of this subgroup, but has revealed the existence of others. In addition, nonaplanatic systems of major potential interest are discussed. These include systems of predecided geometrical arrangement, telecentric systems, inside-out systems, parfocal systems, and others. Means of extending the theory to include nonspherical surfaces are discussed.
Seymour Rosin, "Inverse Cassegrainian Systems," Appl. Opt. 7, 1483-1497 (1968)