In this chapter we discuss various derivatives of the Schmidt type of telescope, including Schmidt-Cassegrain, Baker-Schmidt, and Bouwers-Maksutov systems. Each of these is a type of catadioptric telescope in which a full-aperture refracting element provides the aberration correction needed to get good imagery over a wide field. Given this definition, the classical Schmidt telescope is also of this type.
The Schmidt-Cassegrain, as the name suggests, is a two-mirror system with an aspheric corrector in the collimated beam ahead of the primary mirror. BakerSchmidt systems are a subclass of the Schmidt-Cassegrain with a flat focal surface, of which examples of two specific types are given. The Bouwers-Maksutov type is one in which the aspheric corrector is replaced by a meniscus lens with spherical surfaces. This type of corrector, in combination with one or two mirrors, is the basis for a wide variety of wide-field systems. The design parameters are given for selected examples of systems using a meniscus corrector.
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