Editing Collimator (section)

==Optical collimators==
{{Main|Collimated light}}
[[File:Collimator.svg|thumb|right|An example of an optical collimator with a bulb, an aperture (A), and a plano-convex lens (L)]]
In [[optics]], a collimator may consist of a [[curved mirror]] or [[lens (optics)|lens]] with some type of light source and/or an image at its [[focus (optics)|focus]]. This can be used to replicate a target focused at [[infinity]] with little or no [[parallax]].

In [[lighting]], collimators are typically designed using the principles of [[nonimaging optics]].<ref name="IntroNio2e">{{cite book |first= Julio |last= Chaves |title= Introduction to Nonimaging Optics, Second Edition |url=https://books.google.com/books?id=e11ECgAAQBAJ |publisher= [[CRC Press]] |year= 2015 |isbn= 978-1482206739}}</ref>

Optical collimators can be used to calibrate other optical devices,<ref>[http://www.rondexter.com/professional/equipment/collimators.htm "''Collimators and Auto Collimators''" by Ron Dexter]</ref> to check if all elements are aligned on the [[optical axis]], to set elements at proper focus, or to align two or more devices such as [[binoculars]] or [[gun barrel]]s and [[sight (device)|gunsights]].<ref>{{Cite web |url=https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2001016548 |title="Magnetic lightweight collimator" |access-date=2025-05-22|website=Patentscope|publisher=WIPO }}</ref> A surveying camera may be collimated by setting its [[fiduciary marker]]s so that they define the principal point, as in [[photogrammetry]].

Optical collimators are also used as [[gun sight]]s in the [[collimator sight]], which is a simple optical collimator with a cross hair or some other [[reticle]] at its focus. The viewer only sees an image of the reticle. They have to use it either with both eyes open and one eye looking into the collimator sight, with one eye open and moving the head to alternately see the sight and the target, or with one eye to partially see the sight and target at the same time.<ref>[https://archive.org/details/elementaryoptics00unitrich/page/84 <!-- quote=Collimator sight. --> Elementary optics and applications to fire control instruments: May, 1921 By United States. Army. Ordnance Dept, page 84]</ref>{{what|reason=This sentence had wrong or missing words. I hope I've corrected it properly. It remains a bit confusing|date=June 2015}} Adding a [[beam splitter]] allows the viewer to see the reticle and the [[field of view]], making a [[reflector sight]].

Collimators may be used with [[laser diode]]s and [[carbon-dioxide laser|CO<sub>2</sub> cutting lasers]]. Proper collimation of a laser source with long enough [[coherence length]] can be verified with a [[shearing interferometer]].