Editing Depth of field (section)

==Diffraction and DOF==
[[Diffraction]] causes images to lose sharpness at high {{nowrap|f-numbers}} (i.e., narrow aperture stop opening sizes), and hence limits the potential depth of field.{{sfn|Gibson|1975| p=64}} (This effect is not considered in the above formula giving approximate {{abbr|DOF|depth of field}} values.) In general photography this is rarely an issue; because large {{nowrap|f-numbers}} typically require long exposure times to acquire acceptable image brightness, [[motion blur]] may cause greater loss of sharpness than the loss from diffraction. However, diffraction is a greater issue in close-up photography, and the overall image sharpness can be degraded as photographers are trying to maximize depth of field with very small apertures.{{sfn|Gibson|1975| p=53}}{{sfn|Lefkowitz|1979| p=84}}

Hansma and Peterson have discussed determining the combined effects of defocus and diffraction using a root-square combination of the individual blur spots.{{sfn|Hansma|1996}}{{sfn|Peterson|1996}} Hansma's approach determines the {{nowrap|f-number}} that will give the maximum possible sharpness; Peterson's approach determines the minimum {{nowrap|f-number}} that will give the desired sharpness in the final image and yields a maximum depth of field for which the desired sharpness can be achieved.{{Efn|Peterson does not give a closed-form expression for the minimum {{nowrap|f-number}}, though such an expression obtains from simple algebraic manipulation of his Equation&nbsp;3.}} In combination, the two methods can be regarded as giving a maximum and minimum {{nowrap|f-number}} for a given situation, with the photographer free to choose any value within the range, as conditions (e.g., potential motion blur) permit. Gibson gives a similar discussion, additionally considering blurring effects of camera lens aberrations, enlarging lens diffraction and aberrations, the negative emulsion, and the printing paper.{{sfn|Gibson|1975|p=64}}{{Efn|The analytical section at the end of [[#CITEREFGibson1975|Gibson (1975)]] was originally published as "Magnification and Depth of Detail in Photomacrography" in the ''Journal of the Photographic Society of America'', Vol. 26, No. 6, June 1960.}} Couzin gave a formula essentially the same as Hansma's for optimal {{nowrap|f-number}}, but did not discuss its derivation.{{sfn|Couzin|1982}}

Hopkins,{{sfn|Hopkins|1955}} Stokseth,{{sfn|Stokseth|1969}} and Williams and Becklund{{sfn|Williams|Becklund|1989}} have discussed the combined effects using the [[modulation transfer function]].<ref>"[http://www.largeformatphotography.info/articles/DoFinDepth.pdf Depth of Field in Depth]", Jeff Conrad</ref><ref>"[http://www.faqs.org/faqs/rec-photo/lenses/tutorial/ Photographic Lenses Tutorial]", David M. Jacobson, 26 October 1996</ref>