An interesting article: "New optical systems for small-size telescopes".

The deficiencies of the popular mass-produced telescopes of the Schmidt-Cassegrain design include their low aperture ratio and narrow spectral range. The novel systems for Cassegrain telescopes with a meniscus corrector proposed here are free of these deficiencies. Two such systems are described: a system with corrector lenses made from the same material and a system with corrector lenses made from different materials. The systems are technologically convenient (all the surfaces are spherical) and are distinguished by small lens diameters (down to 1/3 of the effective aperture), compactness, a high aperture ratio (up to 1:6.5-1:7), high-quality aberration correction, and a broad spectral range (400-900 nm), which is sufficient for working with modern photographic materials and CCD arrays.

Full article URL: http://www.telescopes.ru/articles/article1.phtml