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Ritchey-Chretien telescopes: dream telescopes for every astro-photographer!
Of all the Cassegrain mirror telescope versions, the Ritchey-Chretien variant offers the highest level of optical error correction. A Ritchey-Chretien telescope is not only designed to ensure no spherical aberration, but also no coma. In practice this means that stars are not only perfectly in focus in the center of the image, but also right across the field of view. Since no additional coma corrector is required, there is also no chromatic aberration - the colour error typically experienced with lenses.
In an RC telescope the main mirror is fixed and focusing is carried out using the focuser. In an SC telescope the mirror is movable to enable focusing which can lead to image shifting.
The fact that the Ritchey-Chretien system is the mirror configuration with the highest levels of correction has meant that almost all large research telescopes in the world are RC telescopes. The hyperbolic primary and secondary mirrors that give the advantage of high image quality are very expensive to produce. For this reason an RC telescope was, even for wealthy amateur astronomers, until recently a dream that could never be realised. In the meantime Ritchey-Chretien telescopes are now available in the same price range as simpler Cassegrain systems.
This RC telescope is especially optimised for astrophotography; a large secondary mirror provides the necessary illumination of the image field, even for full-frame cameras. The combination of temperature stable quartz mirror substrate ("low thermal expansion glass") with highly-reflective coating ensures bright images and alignment accuracy!
