Flare in Camera Lens
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Internal reflection of light, called
flare, within a complex lens produces stray light rays that tend to
"fog" the camera sensor or whole film frame with a slight overall
exposure. With black-and-white films, the most obvious effect in
printing is an overall lower picture contrast; color films may also
display a bluish color cast, because the short, blue wavelengths are
most easily scattered. The tendency toward flare is reduced in lens
manufacture by coating the glass-to-air surfaces with antireflective
materials. Residual effects of simple lens flare are reduced in
photography by closing down the lens aperture, since the effect is at
its worst at a wide open aperture.
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Zoom lenses are particularly likely to
display flare effects, because of their relatively large number of
glass-to-air surfaces, and because to vary the focal length certain
lens groups must move with respect to one another and cannot be kept in
an optimum relationship. However, closing the aperture a stop or two
takes care of the matter in the better designs.
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Common with zoom lenses are excessive
flare effects that produce multiple images of a light source when the
lens is aimed toward or close to the light. (Such effects are often
deliberately used in the more dramatic television programs.) If they
are not wanted for their pictorial effects, they can be avoided by
using care in backlighted photography. A lens shade will also help,
especially one that can be adjusted to follow closely the image edges
and thereby exclude from the lens any light not actually making up part
of the image.
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