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Reflecting telescope

A reflecting telescope (reflector) is an optical telescope which uses mirrors, rather than lenses, to reflect light. Newton designed the first reflector; in order to solve problems, such as chromatic aberration, which occur with refracting telescopes. The traditional two-mirrored reflector is known as a Newtonian reflector.

While still used in amateur astronomy, professionals now tend to use prime focus, Cassegrain focus, and coudé focus designs. On Earth (by 2001), there were at least 49 reflectors with primary mirrors having diameters of 2m+.

Table of contents
1 Technical Difficulties
2 Notable Reflectors
3 The Prime Focus
4 The Cassegrain Focus
5 The Coudé Focus

Technical Difficulties

Reflecting telescopes do not have as many technical issues, as do the refracting telescopes; however, they are also more expensive. In addition, reflectors which have spherical mirrors (rather than parabolic mirrors) tend to suffer from spherical aberrations. These aberrations can be corrected with a Schmidt corrector plate; however, corrected non-parabolic reflectors still lack the magnification-power of parabolic reflectors.

Notable Reflectors

The Prime Focus

In a prime focus design, the
astronomer sits inside the telescope, at the focal point of the reflected light.

The Cassegrain Focus

Designs with a Cassegrain focus have a hole drilled through the primary mirror and a mirror, placed where the astronomer would sit in a prime focus telescope, refleces light through the hole.

The Coudé Focus

In a coudé design, the design is similar to the Cassegrain except no hold is drilled in the primary mirror; instead, a third mirror reflects the light to the side.