Editing Depth of field (section)

==Factors affecting depth of field==
[[Image:Depth of field illustration.svg|thumb|Effect of aperture on blur and DOF (Depth of Field). The points in focus&nbsp;('''2''') project points onto the image plane&nbsp;('''5'''), but points at different distances&nbsp;('''1''' and '''3''') project blurred images, or [[circle of confusion|circles of confusion]]. Decreasing the aperture size&nbsp;('''4''') reduces the size of the blur spots for points not in the focused plane, so that the blurring is imperceptible, and all points are within the {{abbr|DOF|depth of field}}.]]

For cameras that can only focus on one object distance at a time, depth of field is the distance between the nearest and the farthest objects that are in acceptably sharp focus in the image.{{sfn|Salvaggio|Stroebel|2009| pp=110-}} "Acceptably sharp focus" is defined using a property called the "[[circle of confusion]]".

The depth of field can be determined by [[focal length]], distance to subject (object to be imaged), the acceptable circle of confusion size, and aperture.<ref name="LondonStone2016">{{Cite book|author1=Barbara London|author2=Jim Stone|author3=John Upton|title=Photography|edition= 8th|year=2005|publisher=Pearson|isbn=978-0-13-448202-6|pages=58}}</ref> Limitations of depth of field can sometimes be overcome with various techniques and equipment. The approximate depth of field can be given by:

<math display="block">
\text{DOF} \approx \frac{2u^2Nc}{f^2} 
</math>

for a given maximum acceptable circle of confusion {{mvar|c}}, focal length {{mvar|f}}, [[f-number]] {{mvar|N}}, and distance to subject {{mvar|u}}.<ref name="AllenTriantaphillidou2011">{{Cite book|author1=Elizabeth Allen|author2=Sophie Triantaphillidou|title=The Manual of Photography|url=https://books.google.com/books?id=IfWivY3mIgAC&pg=PA111|year=2011|publisher=Taylor & Francis|isbn=978-0-240-52037-7|pages=111–}}</ref><ref>{{Cite web |title=Depth of field |url=https://graphics.stanford.edu/courses/cs178/applets/dof.html |website=Stanford Computer Graphics Laboratory}}</ref>

As distance or the size of the acceptable circle of confusion increases, the depth of field increases; however, increasing the size of the aperture (i.e., reducing {{nowrap|f-number}}) or increasing the focal length reduces the depth of field. Depth of field changes linearly with {{nowrap|f-number}} and circle of confusion, but changes in proportion to the square of the distance to the subject and inversely in proportion to the square of the focal length. As a result, photos taken at extremely close range (i.e., so small {{mvar|u}}) have a proportionally much smaller depth of field.

Rearranging the {{abbr|DOF|depth of field}} equation shows that it is the ratio between distance and focal length that affects {{abbr|DOF|depth of field}};

<math display="block">
\text{DOF} \approx 2Nc\left(\frac{u}{f}\right)^2=2Nc\left(1 - \frac{1}{M_T}\right)^2
</math>

Note that <math display="inline">M_T = -\frac{f}{u - f}</math> is the [[Magnification#Single lens|transverse magnification]] which is the ratio of the lateral image size to the lateral subject size.<ref>{{Cite book |last=Hecht |first=Eugene |title=Optics |publisher=Pearson |year=2017 |isbn=978-1-292-09693-3 |edition=5th |pages=172 |chapter=5.2.3 Thin Lenses}}</ref>

[[Sensor size|Image sensor size]] affects {{abbr|DOF|depth of field}} in counterintuitive ways. Because the circle of confusion is directly tied to the sensor size, decreasing the size of the sensor while holding focal length and aperture constant will {{em|decrease}} the depth of field (by the crop factor). The resulting image however will have a different field of view. If the focal length is altered to maintain the field of view, while holding the {{em|f-number constant}}, the change in focal length will counter the decrease of {{abbr|DOF|depth of field}} from the smaller sensor and {{em|increase}} the depth of field (also by the crop factor). However, if the focal length is altered to maintain the field of view, while holding the {{em|aperture diameter constant}}, the {{abbr|DOF|depth of field}} will remain constant. <ref>{{Cite web |last= Nasse |first= H. H. |date= March 2010 |title= Depth of Field and Bokeh |type= Whitepaper |url=https://lenspire.zeiss.com/photo/app/uploads/2018/04/Article-Bokeh-2010-EN.pdf |website= Zeiss Lenspire}}</ref><ref>{{Cite web |title=Digital Camera Sensor Sizes: How it Influences Your Photography |url=https://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm |website= Cambridge In Colour}}</ref><ref>{{Cite web |last= Malan |first= Francois |date= 6 April 2018 |title= Sensor Size, Perspective and Depth of Field |url= https://photographylife.com/sensor-size-perspective-and-depth-of-field |website= Photography Life }}</ref><ref>{{Cite web |last1= Vinson |first1= Jason |date= 22 January 2016 |title= The Smaller the Sensor Size, the Shallower Your Depth of Field |url= https://fstoppers.com/education/smaller-sensor-size-shallower-your-depth-field-110547 |website= Fstoppers |language= en}}</ref>

===Effect of lens aperture===
For a given subject framing and camera position, the {{abbr|DOF|depth of field}} is controlled by the lens aperture diameter, which is usually specified as the [[f-number]] (the ratio of lens focal length to aperture diameter). Reducing the aperture diameter (increasing the {{nowrap|f-number}}) increases the {{abbr|DOF|depth of field}} because only the light travelling at shallower angles passes through the aperture so only cones of rays with shallower angles reach the image plane. In other words, the [[circle of confusion|circles of confusion]] are reduced or increasing the {{abbr|DOF|depth of field}}.<ref>{{Cite web| url = http://physicssoup.wordpress.com/2012/05/18/why-does-a-small-aperture-increase-depth-of-field/| title = Why Does a Small Aperture Increase Depth of Field?| date = 18 May 2012}}{{Self-published source|date=February 2024}}</ref>

For a given size of the subject's image in the focal plane, the same {{nowrap|f-number}} on any focal length lens will give the same depth of field.<ref>{{Cite web |date= 13 January 2009 |last= Reichmann |first= Michael |title= DOF2 |url= https://luminous-landscape.com/dof2// |website= Luminous Landscape}}</ref> This is evident from the above {{abbr|DOF|depth of field}} equation by noting that the ratio {{math|''u''/''f''}} is constant for constant image size. For example, if the focal length is doubled, the subject distance is also doubled to keep the subject image size the same. This observation contrasts with the common notion that "focal length is twice as important to defocus as f/stop",<ref>{{Cite web| url = https://www.kenrockwell.com/sony/lenses/50mm-f12.htm| title = Ken Rockwell}}{{Self-published source|date=February 2024}}</ref> which applies to a constant subject distance, as opposed to constant image size.

Motion pictures make limited use of aperture control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors (e.g., scenes inside a building) and another for exteriors (e.g., scenes in an area outside a building), and adjust exposure through the use of camera filters or light levels. Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.

{{Multiple image
| align = center
| direction = 
| width = 250
| footer = Depth of field for different values of aperture using 50{{nbsp}}mm objective lens and full-frame DSLR camera. Focus point is on the first blocks column.<ref name="photoskop">{{Cite web |url=http://www.photoskop.com/player.html?l=all&ch=3&sec=0 |title=photoskop: Interactive Photography Lessons |date=April 25, 2015}}</ref>{{Better source needed|reason= Citation is to an Adobe Flash animation, which is dead.|date=February 2024}}
| image1 = Dof blocks f1_4.jpg
| caption1 = Aperture{{nbsp}}= {{f/|1.4}}. {{abbr|DOF|depth of field}}{{nbsp}}= 0.8{{nbsp}}cm
| image2 = Dof blocks f4_0.jpg
| caption2 = Aperture{{nbsp}}= {{f/|4.0}}. {{abbr|DOF|depth of field}}{{nbsp}}= 2.2{{nbsp}}cm
| image3 = Dof blocks f22.jpg
| caption3 = Aperture{{nbsp}}= {{f/|22}}. {{abbr|DOF|depth of field}}{{nbsp}}= 12.4{{nbsp}}cm
}}

=== Effect of circle of confusion===
Precise focus is only possible at an exact distance from a lens;{{Efn|Strictly, at an exact distance from a plane.}} at that distance, a point object will produce a small spot image. Otherwise, a point object will produce a larger or blur spot image that is typically and approximately a circle. When this circular spot is sufficiently small, it is visually indistinguishable from a point, and appears to be in focus. The diameter of the largest circle that is indistinguishable from a point is known as the [[acceptable circle of confusion]], or informally, simply as the circle of confusion.

The acceptable circle of confusion depends on how the final image will be used. The circle of confusion as 0.25&nbsp;mm for an image viewed from 25&nbsp;cm away is generally accepted.{{sfn|Savazzi|2011|p=109}}

For [[35mm movie film|35{{nbsp}}mm]] motion pictures, the image area on the film is roughly 22&nbsp;mm by 16&nbsp;mm. The limit of tolerable error was traditionally set at {{convert|0.05|mm|in|abbr=on}} diameter, while for [[16 mm film|16&nbsp;mm film]], where the size is about half as large, the tolerance is stricter, {{convert|0.025|mm|in|abbr=on}}.<ref>{{Cite book|title=Film and Its Techniques|date=1966|publisher=University of California Press|page=56|url=https://books.google.com/books?id=Ocfs3ZsLresC&q=35+mm+motion+picture+film+circle+of+confusion&pg=PA56|access-date=24 February 2016}}</ref> More modern practice for 35&nbsp;mm productions set the circle of confusion limit at {{convert|0.025|mm|in|abbr=on}}.<ref>{{Cite book|author=Thomas Ohanian and Natalie Phillips|title=Digital Filmmaking: The Changing Art and Craft of Making Motion Pictures|date=2013|publisher=CRC Press|isbn=9781136053542|page=96|url=https://books.google.com/books?id=usMqBgAAQBAJ&q=35+mm+motion+picture+film+circle+of+confusion&pg=PA96|access-date=24 February 2016}}</ref>

===Camera movements===
{{See also|View camera}}

The term "camera movements" refers to swivel (swing and tilt, in modern terminology) and shift adjustments of the lens holder and the film holder. These features have been in use since the 1800s and are still in use today on view cameras, technical cameras, cameras with tilt/shift or perspective control lenses, etc. Swiveling the lens or sensor causes the plane of focus (POF) to swivel, and also causes the field of acceptable focus to swivel with the {{abbr|POF|plane of focus}}; and depending on the {{abbr|DOF|depth of field}} criteria, to also change the shape of the field of acceptable focus. While calculations for {{abbr|DOF|depth of field}} of cameras with swivel set to zero have been discussed, formulated, and documented since before the 1940s, documenting calculations for cameras with non-zero swivel seem to have begun in 1990.

More so than in the case of the zero swivel camera, there are various methods to form criteria and set up calculations for {{abbr|DOF|depth of field}} when swivel is non-zero. There is a gradual reduction of clarity in objects as they move away from the {{abbr|POF|plane of focus}}, and at some virtual flat or curved surface the reduced clarity becomes unacceptable. Some photographers do calculations or use tables, some use markings on their equipment, some judge by previewing the image.

When the {{abbr|POF|plane of focus}} is rotated, the near and far limits of {{abbr|DOF|depth of field}} may be thought of as wedge-shaped, with the apex of the wedge nearest the camera; or they may be thought of as parallel to the {{abbr|POF|plane of focus}}.{{sfn|Merklinger|1993|pp=49–56}}{{sfn|Tillmanns|1997|p=71}}