Editing Optics (section)

===Photography===
{{Main|Science of photography}}
[[File:Jonquil flowers at f32.jpg|thumb|right|upright=1.35|Photograph taken with aperture {{f/}}32]]
[[File:Jonquil flowers at f5.jpg|thumb|right|upright=1.35|Photograph taken with aperture {{f/}}5]]
The optics of photography involves both lenses and the medium in which the electromagnetic radiation is recorded, whether it be a [[photographic plates|plate]], [[photographic film|film]], or charge-coupled device. Photographers must consider the [[Reciprocity (photography)|reciprocity]] of the camera and the shot which is summarized by the relation

:Exposure ∝ ApertureArea × ExposureTime × SceneLuminance<ref>
{{cite book
|title=Investigations on the Theory of the Photographic Process
|author1=Samuel Edward Sheppard  |author2=Charles Edward Kenneth Mees
 |name-list-style=amp |publisher=Longmans, Green and Co
|year=1907
|page = [https://archive.org/details/investigationso01meesgoog/page/n232 214]
|url = https://archive.org/details/investigationso01meesgoog
}}</ref>

In other words, the smaller the aperture (giving greater depth of focus), the less light coming in, so the length of time has to be increased (leading to possible blurriness if motion occurs). An example of the use of the law of reciprocity is the [[Sunny 16 rule]] which gives a rough estimate for the settings needed to estimate the proper [[exposure (photography)|exposure]] in daylight.<ref>{{cite book|title=Mastering Black-and-White Photography|author=B.J. Suess|publisher=Allworth Communications|year=2003|isbn=978-1-58115-306-4|url=https://books.google.com/books?id=7LaRPNINH_YC&pg=PT112}}</ref>

A camera's aperture is measured by a unitless number called the [[f-number]] or f-stop, {{f/}}#, often notated as <math>N</math>, and given by
:<math>f/\# = N = \frac fD \ </math>
where <math>f</math> is the focal length, and <math>D</math> is the diameter of the entrance pupil. By convention, "{{f/}}#" is treated as a single symbol, and specific values of {{f/}}# are written by replacing the [[number sign]] with the value. The two ways to increase the f-stop are to either decrease the diameter of the entrance pupil or change to a longer focal length (in the case of a [[zoom lens]], this can be done by simply adjusting the lens). Higher f-numbers also have a larger [[depth of field]] due to the lens approaching the limit of a pinhole camera which is able to focus all images perfectly, regardless of distance, but requires very long exposure times.<ref>{{cite book|title=Basic Photography|author=M.J. Langford|isbn=978-0-240-51592-2|year=2000|publisher=Focal Press|url=https://archive.org/details/basicphotography00lang}}</ref>

The field of view that the lens will provide changes with the focal length of the lens. There are three basic classifications based on the relationship to the diagonal size of the film or sensor size of the camera to the focal length of the lens:<ref name="Bruce Warren, Photography, page 71">{{cite book |first=Bruce |last=Warren |title=Photography |url=https://books.google.com/books?id=sbdGeFem1zwC&pg=PA71 |year=2001 |publisher=Cengage Learning |isbn=978-0-7668-1777-7 |page=71 |url-status=live |archive-url=https://web.archive.org/web/20160819020407/https://books.google.com/books?id=sbdGeFem1zwC&pg=PA71 |archive-date=2016-08-19 }}</ref>
* [[Normal lens]]: angle of view of about 50° (called ''normal'' because this angle considered roughly equivalent to human vision<ref name="Bruce Warren, Photography, page 71"/>) and a focal length approximately equal to the diagonal of the film or sensor.<ref>{{cite book|title=View Camera Technique|author=Leslie D. Stroebel|publisher=Focal Press|year=1999|isbn=978-0-240-80345-6|url=https://books.google.com/books?id=71zxDuunAvMC&pg=PA136}}</ref> <!-- It's generally accepted that 50mm is a bit longer than "normal" for 35mm film; I've based this on 75mm with 6×4cm. Maybe the angle of width, rather than diagonal, is better? -->
* [[Wide-angle lens]]: angle of view wider than 60° and focal length shorter than a normal lens.<ref>{{cite book|title=Using the View Camera|author=S. Simmons|publisher=Amphoto Books|year=1992|isbn=978-0-8174-6353-3|page=35}}</ref>
* [[Long focus lens]]: angle of view narrower than a normal lens. This is any lens with a focal length longer than the diagonal measure of the film or sensor.<ref>{{cite book |author=Sidney F. Ray |title=Applied Photographic Optics: Lenses and Optical Systems for Photography, Film, Video, Electronic and Digital Imaging |url=https://books.google.com/books?id=cuzYl4hx-B8C&pg=PA294 |year=2002 |publisher=Focal Press |isbn=978-0-240-51540-3 |page=294 |url-status=live |archive-url=https://web.archive.org/web/20160819003154/https://books.google.com/books?id=cuzYl4hx-B8C&pg=PA294 |archive-date=2016-08-19 }}</ref> The most common type of long focus lens is the [[telephoto lens]], a design that uses a special ''telephoto group'' to be physically shorter than its focal length.<ref>{{cite book|url = https://books.google.com/books?id=zqkdNwRxSooC&pg=PA109 |title=The New York Times Guide to Essential Knowledge|author=New York Times Staff|isbn=978-0-312-31367-8|year=2004|publisher=Macmillan}}</ref>

Modern zoom lenses may have some or all of these attributes.

The absolute value for the exposure time required depends on how [[sensitometry|sensitive]] to light the medium being used is (measured by the [[film speed]], or, for digital media, by the [[quantum efficiency]]).<ref>{{cite book|title=Principles of Radiographic Imaging: An Art and a Science|author1=R.R. Carlton |author2=A. McKenna Adler |publisher=Thomson Delmar Learning|year=2000|isbn=978-0-7668-1300-7|url = https://books.google.com/books?id=oA-eBHsapX8C&pg=PA318}}</ref> Early photography used media that had very low light sensitivity, and so exposure times had to be long even for very bright shots. As technology has improved, so has the sensitivity through film cameras and digital cameras.<ref>{{cite book|author=W. Crawford|title=The Keepers of Light: A History and Working Guide to Early Photographic Processes|year=1979|publisher=Morgan & Morgan|location=Dobbs Ferry, NY|isbn=978-0-87100-158-0|page=20}}</ref>

Other results from physical and geometrical optics apply to camera optics. For example, the maximum resolution capability of a particular camera set-up is determined by the [[diffraction limit]] associated with the pupil size and given, roughly, by the Rayleigh criterion.<ref>{{cite book|author=J.M. Cowley|year=1975|title=Diffraction physics|location=Amsterdam|publisher=North-Holland|isbn=978-0-444-10791-6}}</ref>