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Ritchey-Chretien Telescopes


A Ritchey-Chretien telescope, or RC, is technically a reflector, since the Ritchey-Chretien telescope uses mirrors to gather light, but it is a reflector with a Cassegrain configuration. A Cassegrain uses mirrors like a reflector but has a folded optical path like a catadioptric telescope. Because the optical path is folded, the tube of a RC telescope is much shorter, making larger apertures more portable. Most large Ritchey-Chretien telescopes have an open truss tube design rather than a closed tube to decrease the weight of the optical tube as a whole.

The Ritchey-Chretien telescope design uses two hyperbolic mirrors to correct for coma and spherical aberration. Other aberrations, such as astigmatism, can be greatly reduced with an additional field flattener. The majority of telescopes at professional observatories are a Ritchey-Chretien because of their wide, flat fields that are perfect for large CCD or CMOS sensors. Smaller aperture RC telescopes are available for amateur astronomers who wish to work with an instrument that was designed for astro-imaging, including this inexpensive entry-level Ritchey-Chretien, the Apertura 6” f/9 RC OTA.