Digital SLR Camera

Some people easily describe its as light falloff, however according to Vanwalree, vignetting is a photograph or drawing whose edges gradually fade into the surrounding paper is called a vignette. The art of creating such an illustration is a deliberate one. Yet the word vignetting is also used to indicate an unintended darkening of the image corners in a photographic image.

Whereby, Wikipedia is defining the Vignetting as a reduction of an image’s brightness or saturation at the periphery compared to the image center.

“A vignette is often added to an image to draw interest to the center and, in effect, frame the center portion of the photo.”-wikipedia

There are four factor that cause vignetting.

1. Mechanical Vignetting.

When mechanical extensions to a lens protrude into its field of view, the image corners receive less light than they would in the absence of the extension and vignetting occurs. The extension can be too long a lens hood, stacked filters, or a combination. The hood and/or filters obscure the entrance pupil from obliquely incident light and the remedy is obvious: use proper accessories. A single, thick filter can already vignette a wide angle lens so it pays to check on vignetting behavior before filters and lens hoods are purchased.

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2. Natural Vignetting.

Natural vignetting, more properly termed natural light falloff, is inherent to each lens design and becomes more troublesome for wide angle lenses. It is associated with the famous cos4 law of illumination falloff. Contrary to popular belief, the argument for this law is not measured in object space but in image space. It is measured at the rear end of the lens as the angle at which the light impinges upon the film.

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3. Optical Vignetting.

Most photographic lenses exhibit optical vignetting to some degree. The effect is strongest when the lens is used wide open and will disappear when the lens is stopped down by a few stops.

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4. Pixel Vignetting.

Pixel vignetting only affects digital cameras and is caused by angle-dependence of the digital sensors. Light incident on the sensor at a right angle produces a stronger signal than light hitting it at an oblique angle. Most digital cameras use built-in image processing to compensate for optical vignetting and pixel vignetting when converting raw sensor data to standard image formats such as JPEG or TIFF. The use of microlenses over the image sensor can also reduce the effect of pixel vignetting.( Definition from Wikipedia)