Editing Newtonian telescope (section)

===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>