Editing Newtonian telescope (section)

==Variations==

There are several variations on the Newtonian design that add a lens to the system creating a [[Catadioptric system#Catadioptric telescopes|catadioptric telescope]]. This is done to correct [[spherical aberration]]  or reduce cost.

===Schmidt–Newtonian===
{{main|Schmidt–Newtonian telescope}}

[[Image:Schmidt-Newton.png|thumb|right|300px|Schmidt–Newtonian telescope.]]
A Schmidt–Newtonian telescope combines the Newtonian optical design with a full-aperture [[Schmidt corrector plate]] in front of the primary mirror that not only corrects [[spherical aberration]] but can also support the secondary mirror. The resulting system has less [[coma (optics)|coma]] and secondary mirror support induced diffraction effects.<ref name=telOpt>{{cite web|title=Schmidt-Newton telescope|url=http://www.telescope-optics.net/SN.htm|publisher=telescopeOptics.net|accessdate=28 August 2012}}</ref>

===Maksutov–Newtonian===
{{further|Maksutov telescope}}

Similar to a Schmidt–Newtonian, a [[Maksutov telescope|Maksutov]] telescope's [[Meniscus corrector|meniscus shaped corrector]] can be added to the Newtonian configuration, which gives it minimal aberration over a wide [[field of view]], with one-fourth the coma of a similar standard Newtonian and one-half the coma of a Schmidt-Newtonian.<ref>{{cite book |url= https://books.google.com/books?id=x3LvAAAAMAAJ |first1=Harrie G. J. |last1=Rutten |first2=Martin A.M. |last2=van&nbsp;Venrooij |title= Telescope Optics: Evaluation and design|year=1988 |isbn=9780943396187 }}</ref> Diffraction can also be minimized by using a high [[focal ratio]] with a proportionally small diagonal mirror mounted on the corrector.<ref>{{cite book |url= https://books.google.com/books?id=kszsAxOHym0C&pg=PA101|first=Rod |last=Mollise |title= Choosing and Using a New CAT |date=28 February 2009 |page=101|isbn=9780387097725 }}</ref>

===Jones–Bird===
A Jones–Bird Newtonian (sometimes called a Bird–Jones) uses a spherical primary mirror in place of a parabolic one, with spherical aberrations corrected by [[Catadioptric system#Sub-aperture correctors|sub-aperture corrector]] lens<ref>[http://www.telescope-optics.net/sub_aperture_corrector.htm#bottom  10.1.2. Sub-aperture corrector examples: Single-mirror systems  –  Jones-Bird]</ref> usually mounted inside the focusser tube or in front of the secondary mirror. This design reduces the size and cost of the telescope with a shorter overall telescope tube length (with the corrector extending the focal length in a "[[telephoto]]" type layout)  combined with a less costly spherical mirror. Commercially produced versions of this design have been noted to be optically compromised, due to the difficulty of producing a correctly shaped sub-aperture corrector, and are targeted at the inexpensive end of the telescope market.<ref>{{Cite web |url=http://www.whichtelescope.com/ |title=TELESCOPES – OVERVIEW AND TELESCOPE TYPES, CATADIOPTRIC NEWTONIAN |access-date=2014-11-18 |archive-date=2020-08-11 |archive-url=https://web.archive.org/web/20200811162820/http://www.whichtelescope.com/ |url-status=dead }}</ref>