Editing Reflecting telescope (section)

=== Prime focus ===

[[File:Prime focus telescope.svg|right|thumb|250px|A prime focus telescope design. The observer/camera is at the focal point (shown as a red X).]]

In a ''prime focus'' design no secondary optics are used, the image is accessed at the [[Focus (optics)|focal point]] of the [[primary mirror]]. At the focal point is some type of structure for holding a film plate or electronic detector. In the past, in very large telescopes, an observer would sit inside the telescope in an "observing cage" to directly view the image or operate a camera.<ref>{{cite book|author=W. Patrick McCray|title=Giant Telescopes: Astronomical Ambition and the Promise of Technology|url=https://books.google.com/books?id=9mUL9dGn9V4C&pg=PA27|year=2004|publisher=Harvard University Press|isbn=978-0-674-01147-2|page=27}}</ref> Nowadays [[Charge-coupled device|CCD]] cameras allow for remote operation of the telescope from almost anywhere in the world. The space available at prime focus is severely limited by the need to avoid obstructing the incoming light.<ref>{{cite web|url=http://www.ucolick.org/public/telescopes/shane.html#prime|title=Prime Focus}}</ref>

[[Radio telescope]]s often have a prime focus design. The mirror is replaced by a metal surface for reflecting [[radio wave]]s, and the observer is an [[Antenna (electronics)|antenna]].
{{See also|Schmidt camera}}