Vignetting is a widespread photographic problem. It is found in most lenses and certainly in all cheap compact cameras. It is most visible at the corners as a radial loss of brightness, due to lowered exposure. Vignetting is generally undesirable, but it can be used to draw attention to the central subject of the image. There are in fact two aspects to vignetting: The less exposed corners and the bright center, known as the hot spot.
There are several causes of vignetting: 1. Mechanical. 2. Optical. 3. Natural. 4. Pixel.
Mechanical vignetting is typically caused by too thick a stack of filters, or a lens hood attached to the lens, or by secondary lenses. All three may reduce the exposure at the corners and darken them. The size of the aperture determines if the darkening will be abrupt or gradual. Small apertures create a more abrupt vignetting.
Optical vignetting is caused by the lens itself and is inherent in its build-up of multiple lens elements, and also the fact that the lens has a considerable length. Another name for it is 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 of the photo. Zoom lenses and wide angle lenses are particularly prone to this kind of V. The light in the lens is also reduced radially because the rear lens elements are shaded by the front lens elements, thus causing vignetting. One can often cure optical V by reducing the aperture two or three stops. This kind of vignetting can be reduced by using very large front lens elements and this is often done in wide angle lenses. Lastly, the contrast of the film or sensor plays a part: the stronger the contrast, the more pronounced the vignetting
Natural vignetting (also called natural light falloff) is a, well, natural light falloff proportional to the angle the light reaches the sensor or film; it is not caused by the lens. Technically the falloff is proportional to the fourth power of the cosine of the angle that the light reaches 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. At large apertures both optical and natural vignetting are present. The combined effect is often called illumination falloff or radial density.
Pixel vignetting is of course not relevant for film, but only for digital cameras. It is created because most sensors have an angle dependency of the in falling light. Light reaching the sensor at an oblique angle generates a weaker sensor reaction than light reaching it at a right 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 is typically caused by too thick a stack of filters, or a lens hood attached to the lens, or by secondary lenses. All three may reduce the exposure at the corners and darken them. The size of the aperture determines if the darkening will be abrupt or gradual. Small apertures create a more abrupt vignetting.
Optical vignetting is caused by the lens itself and is inherent in its build-up of multiple lens elements, and also the fact that the lens has a considerable length. Another name for it is 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 of the photo. Zoom lenses and wide angle lenses are particularly prone to this kind of V. The light in the lens is also reduced radially because the rear lens elements are shaded by the front lens elements, thus causing vignetting. One can often cure optical V by reducing the aperture two or three stops. This kind of vignetting can be reduced by using very large front lens elements and this is often done in wide angle lenses. Lastly, the contrast of the film or sensor plays a part: the stronger the contrast, the more pronounced the vignetting
Natural vignetting (also called natural light falloff) is a, well, natural light falloff proportional to the angle the light reaches the sensor or film; it is not caused by the lens. Technically the falloff is proportional to the fourth power of the cosine of the angle that the light reaches 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. At large apertures both optical and natural vignetting are present. The combined effect is often called illumination falloff or radial density.
Pixel vignetting is of course not relevant for film, but only for digital cameras. It is created because most sensors have an angle dependency of the in falling light. Light reaching the sensor at an oblique angle generates a weaker sensor reaction than light reaching it at a right 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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What is vignetting in photos and how do you avoid it? Source: vignetting in photos.
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