Photography
Lens flare
A lens flare is a visual artifact caused by light scattering, or flaring, in a lens system. This can happen through light scattered by the imaging mechanism itself, for example through internal reflection and forward scatter from material imperfections in the lens. Lenses with large numbers of elements such as zooms tend to have more lens flare, as they contain a relatively large number of interfaces at which internal scattering may occur. These mechanisms differ from the focused image generation mechanism, which uses rays that are from the reflection of light on the subject to be imaged and propagating along the intended paths in the lens system. There are two types of flare: visible artifacts and glare across the image. The glare makes the image look "washed out" by reducing contrast and color saturation (adding light to dark image regions, and adding white to saturated regions, reducing their saturation). Visible artifacts, usually in the shape of the aperture made by the iris diaphragm, are formed when light follows a pathway through the lens that contains one or more reflections from the lens surfaces. Flare is particularly caused by very bright light sources. Most commonly, this occurs when the lens is aimed toward the Sun (when the Sun is in frame or the lens is pointed sunward), and is reduced by use of a lens hood or other shade. For good-quality optical systems, and for most images (which do not have a bright light shining into the lens), flare is a secondary effect that is widely distributed across the image and thus not visible, although it does reduce contrast. In photography, lens flares are often undesirable, but they may be used intentionally to invoke a sense of drama or realism.
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