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Coudé focus:see telescopetelescope,
traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional optical telescopes, which are the subject of this article, also are used to magnify objects on earth and in astronomy; other types of
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coudé focus(koo -day) See coudé telescope.
a term used to designate the optical system of a telescope in which converging light beams are reflected by one or more plane mirrors such that the focal plane remains fixed for any direction of the telescope's optical axis. Light beams are usually directed to the focal plane through a hollow polar axle. The coude focusing system is used in most large reflecting telescopes, thus making possible stationary mounting of large astronomical spectrographs. For English and German telescope mountings two plane mirrors are required; for American mountings one mirror can be used when observing stars close to the celestial equator, but three must be used for observations far from it.