Editing Vignetting (section)

==Causes==
There are several causes of vignetting. Sidney F. Ray<ref>Sidney F. Ray, Applied photographic optics, 3rd ed., Focal Press (2002) {{ISBN|978-0-240-51540-3}}.</ref> distinguishes the following types:

* Mechanical vignetting
* Optical vignetting
* Natural vignetting

A fourth cause is unique to digital imaging:
* Pixel vignetting

A fifth cause is unique to analog imaging:
* [[Photographic emulsion|Photographic film]] vignetting

===Mechanical vignetting===
Mechanical vignetting occurs when light beams emanating from object points located off-axis (laterally or vertically off from the optical axis of an optical system under consideration) are partially blocked by external objects of the optical system such as thick or stacked filters, secondary lenses, and improper lens hoods. This has the effect of changing the [[entrance pupil]] shape as a function of angle (resulting in the path of light being partially blocked). Darkening can be gradual or abrupt – the smaller the aperture, the more abrupt the vignetting as a function of angle.

When some points on an image receives no light at all due to mechanical vignetting (the paths of light to these image points is completely blocked), then this results in a restriction of the [[field of view|Field of View]] (FOV) – parts of the image are then completely black.

===Optical vignetting===
This type of vignetting is caused by the physical dimensions of a multiple element lens. Rear elements of the lens are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light. The result is a gradual decrease in light intensity towards the image periphery. Optical vignetting is sensitive to the lens [[aperture]] and can often be cured by a reduction in aperture of 2–3 stops. (An ''increase'' in the [[F-number]].)

===Natural vignetting===
Unlike the previous types, natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays. The falloff is approximated by the cos<sup>4</sup> or "cosine fourth" law of illumination fall off. Here, the light fall off is proportional to the fourth power of the [[cosine]] of the angle at which the light impinges on the film or [[sensor array]]. Wide angle rangefinder designs and the lens designs used in compact cameras are particularly prone to natural vignetting. Telephoto lenses, [[Angenieux retrofocus|retrofocus]] wide angle lenses used on [[Single-lens reflex camera|SLR]] cameras, and [[Telecentric lens|telecentric]] designs in general are less troubled by natural vignetting. A gradual grey filter or postprocessing techniques may be used to compensate for natural vignetting, as it cannot be cured by stopping down the lens. Some modern lenses are specifically designed so that the light strikes the image perpendicular or nearly so, eliminating or greatly reducing vignetting.

=== Pixel vignetting ===
Pixel vignetting only affects digital cameras and is caused by angle-dependence of the digital sensors{{Clarify|reason=How is this different from the description of natural vignetting?|date=August 2019}}. Light incident on the sensor at normal incident produces a stronger signal than light hitting it at an oblique angle. Most digital cameras use built-in image processing to compensate for optical vignetting and pixel vignetting when converting raw sensor data to standard image formats such as [[JPEG]] or [[TIFF]]. The use of offset [[microlens]]es over the image sensor can also reduce the effect of pixel vignetting.
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[[Image:Dawn vignetting effect - swifts creek.jpg|thumb|center|650px|Vignetting can be used to artistic effect, as demonstrated in this panorama.]]

[[image:Woy Woy Channel - Vignetted.jpg|thumb|right|220px|Vignetting can be applied in the post-shoot phase with [[digital imaging]] software.]]