Editing Vignetting (section)

===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.