Lens flare
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2008-06-27T22:06:17Z
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[[Image:Lens Flare.jpg|thumb|Photograph of [[NASA]] [[Apollo Lunar Module|lunar lander]] containing lens flare. Besides the obvious flare around the [[Sun]], the light artifacts at the bottom right are also caused by flare.]]
[[Image:Digital camera artifact .jpg|The second sun at the image is the refraction of the Sun from camera lens|250px|thumb]]
[[Image:CCTV Lens flare.jpg|thumb|Lens flare in a [[Closed-circuit television|CCTV]] camera]]
[[Image:Artificial lens flare.png|thumb|Sample of artificial lens flare, as might be used in an animated movie or computer game.]]
[[Image:Edinburgh-Princesstreet2.jpg|thumb|right|Lens flare is extremely difficult to control when a bright light source like the sun is just outside the frame.]]
[[Image:Firework with lens flare.jpg|thumb|right|When the subject of a photo is the light source itself, lens flare can be a desirable and dramatic effect.]]
[[Image:rainbow flare.jpg|thumb|right|Diffraction artifact on a digital picture. The sun is just outside the frame.]]
'''Lens flare''' is the light scattered in [[lens (optics)|lens]] systems through generally unwanted image formation mechanisms, such as internal [[reflection (physics)|reflection]] and [[scattering]] from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image rays. For good optical systems and most images, flare is a secondary effect that is widely distributed across the image and thus not visible. But when an image includes a very bright [[light]] source, flare generated by a bright image region can have enough intensity to become very visible. The light produced by flare mechanisms superimposes broadly across the image, adding light to dark image regions and reducing image contrast.
Lenses with large numbers of elements such as [[Zoom lens|zooms]] tend to exhibit greater lens flare, as they contain multiple surfaces at which unwanted internal scattering occurs.
The spatial distribution of the lens flare typically manifests as several starbursts, rings, or circles in a row across the image or view. Lens flare patterns typically spread widely across the scene and change location with the camera's movement relative to light sources, tracking with the light position and fading as the camera points away from the bright light until it causes no flare at all. The specific spatial distribution of the flare depends on the shape of the [[aperture]] of the image formation elements. For example, if the lens has a 6-bladed aperture, the flare may have a hexagonal pattern.
Such internal scattering is also present in the human eye and manifests in an unwanted veiling [[Glare (vision)|glare]] that is apparent when viewing very bright lights or highly reflective (e.g. [[Specular highlight|specular]]) surfaces.
When a bright light source is shining on the lens but not in its field of view, lens flare appears as a haze that washes out the image and reduces contrast. This can be avoided by shading the lens (the purpose for which [[lens hood]]s are designed). In a studio, a [[Gobo (lighting)|gobo]] or set of [[barn doors]] can be attached to the lighting to keep it from shining on the camera. Modern lenses use lens coatings to reduce the amount reflection and minimize flare.
==Deliberate use==
A lens flare is often deliberately used to invoke a sense of drama. A lens flare is also useful when added to an artificial or modified image composition because it adds a sense of realism, implying that the image is an un-edited original photograph of a "real life" scene.
For both of these reasons (implying realism and/or drama) artificial lens flare is a common effect in various graphics editing programs, although its use can be a point of contention among professional [[graphic design]]ers{{Fact|date=September 2007}}. Lens flare was one of the first special effects developed for computer graphics because it is the result of relatively simple optical principles. During the mid- to late-1990s, it was a popular graphical effect for [[video game|computer and video game]]s, and is now accompanied by other more complex atmospheric effects that add a greater sense of realism{{Fact|date=September 2007}}.
==Diffraction artifact in digital cameras==
One form of flare is specific to [[digital cameras]]. With the sun shining on an unprotected lens, a group of small rainbows appears. This artifact is formed by internal diffraction on the [[image sensor]], which acts like a [[diffraction grating]]. Unlike true lens flare, this artifact is not visible in the eyepiece of a digital [[SLR camera]], making it more difficult to avoid.
== External links ==
{{Commons|LENS FLARE|Lens flares}}
*[http://valuca.piczo.com/LensFlare?cr=1&linkvar=000044 valuca.piczo.com] - A colection of some great pictures with LENS FLARE (misinterpretation for UFOs / examples)
==See also==
* [[Bokeh]], a source of circles around out-of-focus bright points, also due in part to the internals of the lens.
* [[Diffraction spike]], a type of lens flare seen in some [[telescope]]s
* [[Anti-reflective coating]], used to reduce lens flare and produces the red and green colors common in lens flare.
[[Category:Science of photography]]
[[Category:Lenses]]
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