Vignetting

s such as this shot taken with a Holga. (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). 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 zoom lenses, vignetting may occur all along the zoom range, depending on the aperture and the focal length.…

s such as this shot taken with a Holga.]] (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).]] 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 zoom 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 3EV. ==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 ===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 4 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, retrofocus wide angle lenses used on SLR cameras, and 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. ==See also== Dodging and burning Feathering Flat-field correction Metering mode Vignette (philately) ==Footnotes== ==References== Catrysse, Peter B.; Xinqiao Liu, and Abbas El Gamal: "QE Reduction due to Pixel Vignetting in CMOS Image Sensors"; ; in Morley M. Blouke, Nitin Sampat, George M. Williams Jr., Thomas Yeh (ed.): Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications, Proceedings of SPIE Vol. 3965 (2000). Olsen, Doug; Dou, Changyong; Zhang, Xiaodong; Hu, Lianbo; Kim, Hojin; Hildum, Edward. 2010. "Radiometric Calibration for AgCam" Remote Sens. 2, no. 2: 464–477. Zheng, Yuanjie; Stephen Lin, and Sing Bing Kang, Single-Image Vignetting Correction; IEEE Conference on Computer Vision and Pattern Recognition 2006

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