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Cassegrain reflector

(Cassegrain telescope)
(reflector telescope with convex secondary mirror)

A Cassegrain reflector telescope is a reflector telescope with a convex secondary mirror that reflects the image through a hole in the primary mirror. Or, often in the case of a radio telescope, the focal plane can be located in front of the primary reflector. Also, the primary reflector may be asymmetric, e.g., just a fraction of a full circle, so as to avoid both a central hole and obstruction.

The classical design is with a parabolic primary mirror and a hyperbolic convex secondary mirror. The advantage of the Cassegrain design over a simple flat mirror is that the focal length can be set so the secondary mirror is small and blocks little incoming light while the focal plane is still behind the primary mirror, e.g., to be used in a hand-held telescope or, for large telescopes, to handle large instruments.


(telescope type,reflector)
Further reading:
http://en.wikipedia.org/wiki/Cassegrain_reflector

Referenced by pages:
Dall-Kirkham telescope
Hale Telescope
Herschel Space Observatory
reflector telescope
Schiefspiegler
Schmidt camera
Shane Telescope

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