Vignetting

The word vignette, from the same root as vine, originally referred to a decorative border in a book.

A photographer may deliberately choose a lens that is known to produce vignetting to obtain the effect, or it may be introduced with the use of special filters or post-processing procedures.

Sidney F. Ray[2] distinguishes the following types: A fourth cause is unique to digital imaging: A fifth cause is unique to analog imaging: 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).

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.

To give a photo a 'retro' look - that it was made with an old camera or lens - one could add an obvious 'vignette' using 'lens correction' or burning in margins by any of several techniques.

To direct the viewers' attention, the bright corners or margins are barely perceptibly darkened.

A vignette is often added to an image to draw interest to the center and to frame the center portion of the photo.
Vignetting is a common feature of photographs produced by toy cameras such as this shot taken with a Holga .
This example shows both vignetting and restricted field of view (FOV). Here a " point-and-shoot camera " is used together with a microscope to create this image. Pronounced vignetting (fall off in brightness towards the edge) is visible as the optical system is not well adapted. A further circular restriction of the FOV is visible (the black area in the image).
Vignetting can be used to artistic effect, as demonstrated in this panorama.
Vignetting can be applied in the post-shoot phase with digital imaging software.