Filters are a key element of professional photography. Filters are available in many types, from specifically sized filters that screw into the end of the lens to mulit-hued elements that slide into a plastic holder mounted to the outside of the lens. The UV filter is one of the most common filters in photography.
Protection
A UV filter is often referred to as a lens-protective filter, since it helps to prevent the lens glass from getting damaged by scratches and dust. UV filters are designed to be left on the lens at all times.
Neutral
A true UV filter is a neutral grade filter, meaning it is untinted. UV filters block UV-B and UV-C bands of light. Blocking these bands leads to less haze in a photograph.
Other UV Filters
Skylight filters are a slight variant on UV filters. They are slightly tinted, usually with a delicate pink cast, and block some of the blue radiation, useful for getting a clearer shot on bright days and at altitude. Skylight filters are also called 1A filters.
Scattered Light and Fringing
Scattered UV light, particularly UV-A, can make objects in a photography look somewhat cloudy. Using a UV filter can help to compensate for this scattering of light. UV filters can also help compensate for an illusion called "purple fringing," where bright purple bands can seem to surround the edges of dark objects in bright light.
Sizes
Most people prefer to get the screw-on UV filters, so for multiple lenses with different diameters for filters, you will need to buy multiple UV filters, one for each lens. In practice, this is a good idea anyway, since the most common use of the UV filter is to protect the lens.
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