Vignetting (V) is a widespread photographic problem. Most lenses and certainly all compact cameras show it. It is most visible at the corners as a radial loss of brightness, due to lowered exposure.Vignetting can be used as an effect to draw attention to the central subject of a picture, but in general it is undesirable. Vignetting actually has two aspects: The common underexposed corners and the bright center, called the hot spot.
There are several causes of vignetting: 1. Mechanical. 2. Optical. 3. Natural. 4. Pixel.
Mechanical vignetting can be caused by three things: too many filters stacked on the lens, too small a lens hood attached to the lens; or secondary lenses. This will reduce the light at the corners and darken them. Depending on the lens aperture, the darkening will be abrupt or gradual. The smaller the aperture, the more abrupt the vignetting.
Optical vignetting is inseparable from the lens itself and is caused partly by the combination of several lens elements, partly by the fact that the lens itself has a considerable length. It is also called artificial vignetting.When lenses are used with a wide open aperture, the length of the lens becomes a problem: the edges of the lens will occlude the edges of the aperture and thus darken the edges. This kind of V is most pronounced in zoom lenses and wide angle lenses. The light in the lens is also reduced radially because the rear lens elements are shaded by the front lens elements, thus causing vignetting. Optical V can often be cured by reducing the aperture two or three stops. Very large front lens elements tend to reduce this kind of vignetting and is typically used in wide angle lenses. Finally should be mentioned that the contrast of the sensor or film also plays a part: the stronger the contrast, the stronger the vignetting.
Natural vignetting, or natural light falloff as it is properly termed, is not caused by the lenses or mechanical issues, but is a natural light falloff proportional to the angle the light reaches the film or sensor. Technically the falloff is proportional to the fourth power of the cosine of the angle of the in-falling light on the film or sensor. Lenses in compact cameras are particularly prone to such falloff. So are wide angle lenses. Telephoto lenses show the least falloff. Both optical and natural vignetting are present at large apertures. The combined effect is often called illumination falloff or radial density.
Pixel vignetting is of course only relevant for digital cameras. It is caused by light angle dependency of the digital sensors.Light hitting the sensor at a right angle produces a stronger impression than light hitting at an oblique angle, thus the corners become underexposed. Digital cameras often have a built-in compensation for this, used when converting the RAW image data to tiff or jpg. If one works with RAW images, one will have to do post-processing to remove pixel V
There are several causes of vignetting: 1. Mechanical. 2. Optical. 3. Natural. 4. Pixel.
Mechanical vignetting can be caused by three things: too many filters stacked on the lens, too small a lens hood attached to the lens; or secondary lenses. This will reduce the light at the corners and darken them. Depending on the lens aperture, the darkening will be abrupt or gradual. The smaller the aperture, the more abrupt the vignetting.
Optical vignetting is inseparable from the lens itself and is caused partly by the combination of several lens elements, partly by the fact that the lens itself has a considerable length. It is also called artificial vignetting.When lenses are used with a wide open aperture, the length of the lens becomes a problem: the edges of the lens will occlude the edges of the aperture and thus darken the edges. This kind of V is most pronounced in zoom lenses and wide angle lenses. The light in the lens is also reduced radially because the rear lens elements are shaded by the front lens elements, thus causing vignetting. Optical V can often be cured by reducing the aperture two or three stops. Very large front lens elements tend to reduce this kind of vignetting and is typically used in wide angle lenses. Finally should be mentioned that the contrast of the sensor or film also plays a part: the stronger the contrast, the stronger the vignetting.
Natural vignetting, or natural light falloff as it is properly termed, is not caused by the lenses or mechanical issues, but is a natural light falloff proportional to the angle the light reaches the film or sensor. Technically the falloff is proportional to the fourth power of the cosine of the angle of the in-falling light on the film or sensor. Lenses in compact cameras are particularly prone to such falloff. So are wide angle lenses. Telephoto lenses show the least falloff. Both optical and natural vignetting are present at large apertures. The combined effect is often called illumination falloff or radial density.
Pixel vignetting is of course only relevant for digital cameras. It is caused by light angle dependency of the digital sensors.Light hitting the sensor at a right angle produces a stronger impression than light hitting at an oblique angle, thus the corners become underexposed. Digital cameras often have a built-in compensation for this, used when converting the RAW image data to tiff or jpg. If one works with RAW images, one will have to do post-processing to remove pixel V
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