Editing Primary mirror (section)

{{short description|Main light-gathering source of reflecting telescope}}
{{More citations needed|date=November 2023}}
[[File:James Webb Primary Mirror.jpg|thumb|right|Six of the 18 primary mirrors of the [[James Webb Space Telescope]] being prepared for [[acceptance testing]].]]
[[File:A20010288000 NASM2017-10014 (cropped).jpg|thumb|right|The correctly ground backup primary mirror built by Eastman Kodak for the Hubble space telescope (the mirror was never coated with a reflective surface, hence its [[Honeycomb mirror|honeycomb]] support structure is visible). It now resides in the [[National Air and Space Museum]] in Washington, DC.<ref>{{cite web |date=2007-08-28 |title=Mirror, Primary Backup, Hubble Space Telescope |url=http://collections.nasm.si.edu/code/emuseum.asp?profile=objects&newstyle=single&quicksearch=A20010288000 |url-status=dead |archive-url=https://web.archive.org/web/20071013111541/http://collections.nasm.si.edu/code/emuseum.asp?profile=objects&newstyle=single&quicksearch=A20010288000 |archive-date=2007-10-13 |access-date=2008-04-26 |website=Smithsonian - National Air and Space Museum |language=en}}</ref>]]
[[File:LBT 3.JPG|thumb|right|The largest non-segmented mirror in an optical telescope in 2009, one of the Large Binocular Telescope's two mirrors.]]

A '''primary mirror''' (or '''primary''') is the principal [[etendue|light-gathering]] surface (the [[objective (optics)|objective]]) of a [[reflecting telescope]].