Editing Lens (section)

== Uses ==
[[File:Steeldive SD8205-2.jpg|thumb|A watch with a plano-convex lens over the date indicator]]

A single convex lens mounted in a frame with a handle or stand is a [[magnifying glass]].

Lenses are used as [[prosthetic]]s for the correction of [[refractive error]]s such as [[myopia]], [[hypermetropia]], [[presbyopia]], and [[Astigmatism (optical systems)|astigmatism]]. (See [[corrective lens]], [[contact lens]], [[eyeglasses]], [[intraocular lens]].) Most lenses used for other purposes have strict [[axial symmetry]]; eyeglass lenses are only approximately symmetric. They are usually shaped to fit in a roughly oval, not circular, frame; the optical centres are placed over the [[human eyeball|eyeballs]]; their curvature may not be axially symmetric to correct for [[Astigmatism (optical systems)|astigmatism]]. [[sunglass lens|Sunglasses' lens]]es are designed to attenuate light; sunglass lenses that also correct visual impairments can be custom made.

Other uses are in imaging systems such as [[monocular]]s, [[binoculars]], [[optical telescope|telescopes]], [[microscope]]s, [[camera]]s and [[Movie projector|projectors]]. Some of these instruments produce a [[virtual image]] when applied to the human eye; others produce a [[real image]] that can be captured on [[photographic film]] or an [[optical sensor]], or can be viewed on a screen. In these devices lenses are sometimes paired up with [[curved mirror]]s to make a [[catadioptric system]] where the lens's spherical aberration corrects the opposite aberration in the mirror (such as [[Schmidt corrector plate|Schmidt]] and [[Meniscus corrector|meniscus]] correctors).

Convex lenses produce an image of an object at infinity at their focus; if the [[sun]] is imaged, much of the visible and infrared light incident on the lens is concentrated into the small image. A large lens creates enough intensity to burn a flammable object at the focal point. Since ignition can be achieved even with a poorly made lens, lenses have been used as [[burning-glass]]es for at least 2400 years.<ref name="The Clouds">{{Cite book |last=Aristophanes |author-link=Aristophanes |title=The Clouds |title-link=The Clouds |date=22 Jan 2013 |publisher=Project Gutenberg |translator-last=Hickie |translator-first=William James |id=EBook #2562 |orig-year=First performed in 423 BC}}[http://www.gutenberg.org/files/2562/2562-h/2562-h.htm] {{Webarchive|url=https://web.archive.org/web/20170628204155/http://www.gutenberg.org/files/2562/2562-h/2562-h.htm|date=28 June 2017}}</ref> A modern application is the use of relatively large lenses to [[concentrator photovoltaics|concentrate solar energy]] on relatively small [[photovoltaic cell]]s, harvesting more energy without the need to use larger and more expensive cells.

[[Radio astronomy]] and [[radar]] systems often use [[dielectric lens]]es, commonly called a [[lens antenna]] to refract [[electromagnetic radiation]] into a collector antenna.

Lenses can become scratched and abraded. [[abrasion (mechanical)|Abrasion]]-resistant coatings are available to help control this.<ref>{{Cite news
 | last = Schottner
 | first = G
 | title = Scratch and Abrasion Resistant Coatings on Plastic Lenses—State of the Art, Current Developments and Perspectives
 | newspaper = [[Journal of Sol-Gel Science and Technology]]
 | pages = 71–79
 | date = May 2003
 | volume = 27
 | doi = 10.1023/A:1022684011222
 }}</ref>