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In a camera, glare is a non-image forming light which may originate from scattering at dust particles, scratches and damaged lens coatings, and from reflections at lens surfaces, the iris diaphragm and lens shoulders, etc. This light usually results in an overall fog, or veil, at the image plane, though in some cases ghosting of the bright parts of the image may occur. Fortunately the tolerances of veiling glare in a camera are much larger than in a visual optical system, since the image contrast can often be maintained by suitable adjustments during exposure and processing.
However steps must be taken to reduce glare so far as is possible. Since reflections at the iris diaphragm frequently account for a large proportion of glare, stopping down the aperture is not necessarily beneficial; thus it should be ensured that the diaphragm as well as the bellows, lens shoulders, etc. in a system are matt black in order to minimise reflectivity. Lens surfaces should be kept free from dust and protected from scratching. The most effective step towards the elimination of glare is the use of coated lenses, particularly in systems having several air-glass surfaces.
Outside the camera glare refers to the reflection of intense light into the camera lens from highly reflective surfaces (such as water, glass, cars). In outdoor photography this glare is avoidable only by changing the camera viewpoint. With artificial light, repositioning the light source or sources helps.
In copying set-ups glare reflected from the surface of the original being copied (even if not shiny) may reach the lens and produce a "hot spot", i.e: specially dense image patch on the negative. The remedy is correct setting up of the lamps at a suitable angle.