In photography and optics, vignetting is a reduction of an image's brightness or saturation toward the periphery compared to the image center. The word vignette, from the same root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a photographic portrait that is clear at the center and fades off toward the edges. A similar effect is visible in photographs of projected images or videos off a projection screen, resulting in a so-called "hotspot" effect. Vignetting is often an unintended and undesired effect caused by camera settings or lens limitations. However, it is sometimes deliberately introduced for creative effect, such as to draw attention to the center of the frame. 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. When using superzoom lenses, vignetting may occur all along the zoom range, depending on the aperture and the focal length. However, it may not always be visible, except at the widest end (the shortest focal length). In these cases, vignetting may cause an exposure value (EV) difference of up to 0.75EV. Causes There are several causes of vignetting. Sidney F. Ray 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 film vignetting Mechanical vignetting Mechanical vignetting occurs when light beams emanating from object points located off-axis are partially blocked by external objects 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 (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 are shaded by elements in front of them, which reduces the effective lens opening