Editing Reflecting telescope (section)

=== Cassegrain focus ===
[[File:Cassegrain-Teleskop.svg|250px|thumb|right|Cassegrain design]]
For telescopes built to the Cassegrain design or other related designs, the image is formed behind the primary mirror, at the focal point of the [[secondary mirror]]. An observer views through the rear of the telescope, or a camera or other instrument is mounted on the rear. Cassegrain focus is commonly used for amateur telescopes or smaller research telescopes. However, for large telescopes with correspondingly large instruments, an instrument at Cassegrain focus must move with the telescope as it slews; this places additional requirements on the strength of the instrument support structure, and potentially limits the movement of the telescope in order to avoid collision with obstacles such as walls or equipment inside the observatory.