Editing Aperture (section)

==In photography==
The aperture stop of a [[photographic lens]] can be adjusted to control the amount of [[light]] reaching the [[Photographic film|film]] or [[image sensor]]. In combination with variation of [[shutter speed]], the aperture size will regulate the film's or image sensor's degree of [[exposure (photography)|exposure]] to light. Typically, a fast shutter will require a larger aperture to ensure sufficient light exposure, and a slow shutter will require a smaller aperture to avoid excessive exposure.

[[File:Aperture diagram.svg|thumb|Diagram of decreasing aperture sizes (increasing [[f-number]]s) for "full stop" increments (an aperture area decrease by a factor of two per full stop increment)]]

A device called a [[diaphragm (optics)|diaphragm]] usually serves as the aperture stop and controls the aperture (the opening of the aperture stop). The diaphragm functions much like the [[Iris (anatomy)|iris]] of the [[Human eye|eye]]&nbsp;– it controls the effective [[diameter]] of the lens opening (called [[pupil]] in the eyes). Reducing the aperture size (increasing the f-number) provides less light to sensor and also increases the [[depth of field]] (by limiting the angle of cone of image light reaching the sensor), which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the f-number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus.

The lens aperture is usually specified as an [[f-number]], the ratio of [[focal length]] to effective aperture diameter (the diameter of the [[entrance pupil]]). A lens typically has a set of marked "f-stops" that the f-number can be set to. A lower f-number denotes a greater aperture which allows more light to reach the film or image sensor. The photography term "one f-stop" refers to a factor of {{radic|2}} (approx. 1.41) change in f-number which corresponds to a {{radic|2}} change in aperture diameter, which in turn corresponds to a factor of 2 change in light intensity (by a factor 2 change in the aperture area).

[[Aperture priority]] is a semi-automatic shooting mode used in cameras. It permits the photographer to select an aperture setting and let the camera decide the shutter speed and sometimes also [[ISO sensitivity]] for the correct exposure. This is also referred to as Aperture Priority Auto Exposure, A mode, AV mode (aperture-value mode), or semi-auto mode.<ref>{{cite web| url=http://elite-cameras.com/articles/aperture-shutter-speed-digital-cameras.php | title=Aperture and shutter speed in digital cameras| work=elite-cameras.com| access-date=20 June 2006 |archive-url = https://web.archive.org/web/20060620033626/http://elite-cameras.com/articles/aperture-shutter-speed-digital-cameras.php |archive-date = 20 June 2006}} (original link no longer works, but page was saved by archive.org)</ref>

Typical ranges of apertures used in photography are about {{f/|2.8}} – {{f/|22}} or {{f/|2}} – {{f/|16}},<ref>{{cite web| url = http://www.photoxels.com/tutorial_aperture.html| title = What is... Aperture?| access-date = 13 June 2010| archive-date = 10 October 2014| archive-url = https://web.archive.org/web/20141010144020/http://www.photoxels.com/tutorial_aperture.html| url-status = dead}}<!-- f/2 instead of f/1.8 is clearer and mathematically more accurate as 1 stop faster than f/2.8 --></ref> covering six stops, which may be divided into wide, middle, and narrow of two stops each, roughly (using round numbers) {{f/|2}} – {{f/|4}}, {{f/|4}} – {{f/|8}}, and {{f/|8}} – {{f/|16}} or (for a slower lens) {{f/|2.8}} – {{f/|5.6}}, {{f/|5.6}} – {{f/|11}}, and {{f/|11}} – {{f/|22}}. These are not sharp divisions, and ranges for specific lenses vary.

===Maximum and minimum apertures===
{{further|Lens speed}}
The specifications for a given lens typically include the maximum and minimum aperture (opening) sizes, for example, {{f/|0.95}} – {{f/|22}}. In this case, {{f/|0.95}} is currently the maximum aperture (the widest opening on a full-frame format for practical use<ref name="wayne">{{Cite web|last=wayne|date=2021-05-03|title=Argus -Laowa f/0.95 Large Aperture Lenses - Ultra-fast lens|url=https://www.venuslens.net/argus-large-aperture-lenses-laowa/|access-date=2021-09-06}}</ref>), and {{f/|22}} is the minimum aperture (the smallest opening). The maximum aperture tends to be of most interest and is always included when describing a lens. This value is also known as the [[lens speed|lens "speed"]], as it affects the exposure time. As the aperture area is proportional to the light admitted by a lens or an optical system, the aperture diameter is proportional to the square root of the light admitted, and thus inversely proportional to the square root of required exposure time, such that an aperture of {{f/|2}} allows for exposure times one quarter that of {{f/|4}}. ({{f/|2}} is 4 times larger than {{f/|4}} in the aperture area.)

[[File:16 minolta 50mm.jpg|thumb|right|The aperture range of a 50 mm Minolta lens, {{f/|1.4}} – {{f/|16}}]]

Lenses with apertures opening {{f/|2.8}} or wider are referred to as "fast" lenses, although the specific point has changed over time (for example, in the early 20th century aperture openings wider than {{f/|6}} were considered fast.<ref>{{Cite web|url=https://lenscross.com/2021/08/basics-of-photography-a-beginners-guide/|title = Basics of Photography: A Beginner's Guide|date = 31 August 2021}}</ref> The fastest lenses for the common [[135 film|35 mm film]] format in general production have apertures of {{f/|1.2}} or {{f/|1.4}}, with more at {{f/|1.8}} and {{f/|2.0}}, and many at {{f/|2.8}} or slower; {{f/|1.0}} is unusual, though sees some use. When comparing "fast" lenses, the [[Film format|image format]] used must be considered. Lenses designed for a small format such as [[Half-frame camera|half frame]] or [[APS-C]] need to project a much smaller [[image circle]] than a lens used for [[Large format (photography)|large format]] photography. Thus the optical elements built into the lens can be far smaller and cheaper.

In exceptional circumstances lenses can have even wider apertures with f-numbers smaller than 1.0; see [[Lens speed#Fast lenses|lens speed: fast lenses]] for a detailed list. For instance, both the current Leica Noctilux-M 50mm ASPH and a 1960s-era Canon 50mm rangefinder lens have a maximum aperture of {{f/|0.95}}.<ref>{{cite web|url=https://gizmodo.com/5048115/leicas-11000-noctilux-50mm-f095-lens-is-a-nightvision-owl-eye-for-your-camera|title=Leica's $11,000 Noctilux 50mm f/0.95 Lens Is a Nightvision Owl Eye For Your Camera|first=John|last=Mahoney|website=gizmodo.com|date=10 September 2008 |access-date=15 April 2018}}</ref> Cheaper alternatives began appearing in the early 2010s, such as the [[Cosina Voigtländer]] {{f/|0.95}} Nokton (several in the {{val|10.5|-|60|u=mm}} range) and {{f/|0.8}} ({{val|29|u=mm}}) Super Nokton manual focus lenses in the for the [[Micro Four-Thirds System]],<ref>{{cite web |title= Micro Four Thirds Mount Lenses |website= Cosina Voigtlander |date= 19 September 2021 |url= https://www.cosina.co.jp/voigtlander/en/micro-four-thirds/ |access-date= 2023-09-15 |archive-url= https://web.archive.org/web/20220521061918/https://www.cosina.co.jp/voigtlander/en/micro-four-thirds/ |archive-date= 2022-05-21 |url-status= live}}</ref> and the [[Venus Optics]] (Laowa) Argus {{val|35|u=mm}} {{f/|0.95}}.<ref name="wayne"/>

Professional lenses for some movie cameras have f-numbers as small as {{f/|0.75}}. [[Stanley Kubrick]]'s film ''[[Barry Lyndon]]'' has scenes shot by candlelight with a [[Carl Zeiss Planar 50mm f/0.7|NASA/Zeiss 50mm f/0.7]],<ref>{{cite magazine |last1= Lightman |first1= Herb A. |last2= DiGiulio |first2= Ed |date= 16 March 2018 |orig-date= March 1976 |magazine= [[American Cinematographer]] |title= Photographing Kubrick's 'Barry Lyndon' |url= https://theasc.com/articles/flashback-barry-lyndon |access-date= 2023-09-15 |archive-url= https://web.archive.org/web/20230207011224/https://theasc.com/articles/flashback-barry-lyndon |archive-date= 2023-02-07 |url-status= live}}</ref> the fastest lens in film history. Beyond the expense, these lenses have limited application due to the correspondingly shallower [[Depth of field|depth of field (DOF)]]&nbsp;– the scene must either be shallow, shot from a distance, or will be significantly defocused, though this may be the desired effect.

Zoom lenses typically have a maximum relative aperture (minimum f-number) of {{f/|2.8}} to {{f/|6.3}} through their range. High-end lenses will have a constant aperture, such as {{f/|2.8}} or {{f/|4}}, which means that the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable maximum relative aperture since it is harder and more expensive to keep the maximum relative aperture proportional to the focal length at long focal lengths; {{f/|3.5}} to {{f/|5.6}} is an example of a common variable aperture range in a consumer zoom lens.

By contrast, the minimum aperture does not depend on the focal length&nbsp;– it is limited by how narrowly the aperture closes, not the lens design&nbsp;– and is instead generally chosen based on practicality: very small apertures have lower sharpness due to diffraction at aperture edges, while the added depth of field is not generally useful, and thus there is generally little benefit in using such apertures. Accordingly, DSLR lens typically have minimum aperture of {{f/|16}}, {{f/|22}}, or {{f/|32}}, while [[large format]] may go down to {{f/|64}}, as reflected in the name of [[Group f/64]]. Depth of field is a significant concern in [[macro photography]], however, and there one sees smaller apertures. For example, the [[Canon MP-E 65mm f/2.8 1-5x Macro lens|Canon MP-E 65mm]] can have effective aperture (due to magnification) as small as {{f/|96}}. The [[Pinhole camera|pinhole]] optic for [[Lensbaby]] creative lenses has an aperture of just {{f/|177}}.<ref>{{cite web|url=http://www.lensbaby.com/optics-pinhole.php |title=Pinhole and Zone Plate Photography for SLR Cameras |work=Lensbaby Pinhole optic |url-status=dead |archive-url=https://web.archive.org/web/20110501093047/http://www.lensbaby.com/optics-pinhole.php |archive-date=1 May 2011 }}</ref>

<gallery>
Image:Jonquil flowers at f32.jpg|{{f/|32}} – small aperture and slow shutter
Image:Jonquil flowers at f5.jpg|{{f/|5.6}} – large aperture and fast shutter
Image:Aperture Example Wall.jpg|{{f/|22}} – small aperture and slower shutter (Exposure time: 1/80)
Image:Aperture Example Wall 2.jpg|{{f/|3.5}} – large aperture and faster shutter (Exposure time: 1/2500)
Image:Povray focal blur animation.gif|Changing a camera's aperture value in half-stops, beginning with {{f/|256}} and ending with {{f/|1}}
Image:Povray focal blur animation mode tan.gif|Changing a camera's aperture diameter from zero to infinity
</gallery>

===Aperture area===
The amount of light captured by an optical system is proportional to the area of the [[entrance pupil]] that is the object space-side image of the aperture of the system, equal to:

:<math>\mathrm{Area} = \pi \left({D \over 2}\right)^2 = \pi \left({f \over 2N}\right)^2 </math>

Where the two equivalent forms are related via the [[f-number]] ''N = f'' / ''D'', with [[focal length]] ''f'' and entrance pupil diameter ''D''.

The focal length value is not required when comparing two lenses of the same focal length; a value of 1 can be used instead, and the other factors can be dropped as well, leaving area proportion to the reciprocal square of the f-number ''N''.

If two cameras of different format sizes and focal lengths have the same [[angle of view]], and the same aperture area, they gather the same amount of light from the scene. In that case, the relative focal-plane [[illuminance]], however, would depend only on the f-number ''N'', so it is less in the camera with the larger format, longer focal length, and higher f-number. This assumes both lenses have identical transmissivity.

===Aperture control===
[[File:Aperture in Canon 50mm f1.8 II lens.jpg|thumb|right|Aperture mechanism of Canon 50mm f/1.8 II lens, with five blades]]
Though as early as 1933 [[Torkel Korling]] had invented and patented for the [[Graflex]] large format reflex camera an automatic aperture control,<ref>{{cite web| url = https://patentimages.storage.googleapis.com/16/ca/43/f0757f2baf705f/US2029238.pdf| title = US patent 2,029,238 Camera Mechanism, Application June 4, 1933}}</ref> not all early 35mm single lens reflex cameras had the feature. With a small aperture, this darkened the viewfinder, making viewing, focusing, and composition difficult.<ref>{{cite book|last=Shipman|first=Carl|title=SLR Photographers Handbook|date=1977|publisher=HP Books|location=Tucson, AZ|isbn=0-912656-59-X|pages=[https://archive.org/details/slrphotographers05ship/page/53 53]|url=https://archive.org/details/slrphotographers05ship/page/53}}</ref> Korling's design enabled full-aperture viewing for accurate focus, closing to the pre-selected aperture opening when the shutter was fired and simultaneously synchronising the firing of a flash unit. From 1956 [[SLR camera]] manufacturers separately developed ''automatic aperture control'' (the [[Miranda T (camera)|Miranda T]] 'Pressure Automatic Diaphragm', and other solutions on the [[Exakta|Exakta Varex IIa]] and [[Praktica|Praktica FX2]]) allowing viewing at the lens's maximum aperture, stopping the lens down to the working aperture at the moment of exposure, and returning the lens to maximum aperture afterward.<ref name="Ray2000-136">Sidney F. Ray. The geometry of image formation. In ''The Manual of Photography: Photographic and Digital Imaging'', 9th ed, pp. 136–137. Ed. Ralph E. Jacobson, Sidney F. Ray, Geoffrey G. Atteridge, and Norman R. Axford. Oxford: Focal Press, 2000. {{ISBN|0-240-51574-9}}</ref> The first SLR cameras with internal ([[Through-the-lens metering|"through-the-lens" or "TTL"]]) meters (e.g., the [[Pentax Spotmatic]]) required that the lens be stopped down to the working aperture when taking a meter reading. Subsequent models soon incorporated mechanical coupling between the lens and the camera body, indicating the working aperture to the camera for exposure while allowing the lens to be at its maximum aperture for composition and focusing;<ref name="Ray2000-136"/> this feature became known as [[open-aperture metering]].

For some lenses, including a few long [[Telephoto lens|telephotos]], lenses mounted on [[Bellows (photography)|bellows]], and [[Perspective control lens|perspective-control and tilt/shift]] lenses, the mechanical linkage was impractical,<ref name="Ray2000-136"/> and automatic aperture control was not provided. Many such lenses incorporated a feature known as a "preset" aperture,<ref name="Ray2000-136"/><ref>B. "Moose" Peterson. ''Nikon System Handbook''. New York: Images Press, 1997, pp. 42–43. {{ISBN|0-929667-03-4}}</ref> which allows the lens to be set to working aperture and then quickly switched between working aperture and full aperture without looking at the aperture control. A typical operation might be to establish rough composition, set the working aperture for metering, return to full aperture for a final check of focus and composition, and focusing, and finally, return to working aperture just before exposure. Although slightly easier than stopped-down metering, operation is less convenient than automatic operation. Preset aperture controls have taken several forms; the most common has been the use of essentially two lens aperture rings, with one ring setting the aperture and the other serving as a limit stop when switching to working aperture. Examples of lenses with this type of preset aperture control are the Nikon PC Nikkor 28&nbsp;mm {{f/|3.5}} and the SMC Pentax Shift 6×7 75&nbsp;mm {{f/|4.5}}. The Nikon PC Micro-Nikkor 85&nbsp;mm {{f/|2.8D}} lens incorporates a mechanical pushbutton that sets working aperture when pressed and restores full aperture when pressed a second time.

Canon [[Canon EF mount|EF]] lenses, introduced in 1987,<ref>[http://www.canon.com/camera-museum/history/canon_story/f_index.html Canon Camera Museum]. Accessed 12 December 2008.
</ref> have electromagnetic diaphragms,<ref>''EF Lens Work III: The Eyes of EOS''. Tokyo: Canon Inc., 2003, pp. 190–191.</ref> eliminating the need for a mechanical linkage between the camera and the lens, and allowing automatic aperture control with the Canon TS-E tilt/shift lenses. Nikon PC-E perspective-control lenses,<ref>[http://www.nikonusa.com/Find-Your-Nikon/Camera-Lenses/Manual/Perspective-Control.page Nikon USA web site] {{webarchive |url=https://web.archive.org/web/20081212065043/http://www.nikonusa.com/Find-Your-Nikon/Camera-Lenses/Manual/Perspective-Control.page |date=12 December 2008 }}. Accessed 12 December 2008.</ref> introduced in 2008, also have electromagnetic diaphragms,<ref>[http://www.nikonusa.com/Assets/Common-Assets/PDF/PCLenses_Compare2008.pdf Nikon PC-E product comparison brochure] {{webarchive |url=https://web.archive.org/web/20081217165006/http://www.nikonusa.com/Assets/Common-Assets/PDF/PCLenses_Compare2008.pdf |date=17 December 2008 }}. Accessed 12 December 2008.</ref> a feature extended to their E-type range in 2013.

===Optimal aperture===
Optimal aperture depends both on optics (the depth of the scene versus diffraction), and on the performance of the lens.

Optically, as a lens is stopped down, the defocus blur at the Depth of Field (DOF) limits decreases but diffraction blur increases. The presence of these two opposing factors implies a point at which the combined blur spot is minimized ([[#CITEREFR Gibson1975|Gibson 1975]], 64); at that point, the <var>f</var>-number is optimal for image sharpness, for this given depth of field<ref>{{cite web|url=http://www.bobatkins.com/photography/technical/diffraction.html|title=Diffraction and Optimum Aperture – Format size and diffraction limitations on sharpness|website=www.bobatkins.com|access-date=15 April 2018}}</ref>&nbsp;– a wider aperture (lower ''f''-number) causes more defocus, while a narrower aperture (higher ''f''-number) causes more diffraction.

As a matter of performance, lenses often do not perform optimally when fully opened, and thus generally have better sharpness when stopped down some&nbsp;– this is sharpness in the plane of [[critical focus]], setting aside issues of depth of field. Beyond a certain point, there is no further sharpness benefit to stopping down, and the diffraction occurred at the edges of the aperture begins to become significant for imaging quality. There is accordingly a sweet spot, generally in the {{f/|4}} – {{f/|8}} range, depending on lens, where sharpness is optimal, though some lenses are designed to perform optimally when wide open. How significant this varies between lenses, and opinions differ on how much practical impact this has.

While optimal aperture can be determined mechanically, how much sharpness is ''required'' depends on how the image will be used&nbsp;– if the final image is viewed under normal conditions (e.g., an 8″×10″ image viewed at 10″), it may suffice to determine the <var>f</var>-number using criteria for minimum required sharpness, and there may be no practical benefit from further reducing the size of the blur spot. But this may not be true if the final image is viewed under more demanding conditions, e.g., a very large final image viewed at normal distance, or a portion of an image enlarged to normal size ([[#CITEREFR Hansma1996|Hansma 1996]]). Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time; see also [[critical sharpness]].