Photographic filter

thumb
A photographic filter is a lens that is used in photography to filter the light. There are different kinds of filters:
Clear filters, commonly known as window glass are put in front of a lens to protect the camera lens.
UV filters are used to reduce the haziness, strong UV filters can be used for warming up certain types of color photos in the shade. They can also correct some of the purple haze on certain digital cameras
Filters are used for color correction; the main use there is to be able to use daylight-type film indoors, or indoor-type film outdoors.
Filters are used to enhance contrast. Examples for this are color filters (red, orange, green,..) in black and white photography or polarizing filters in color photography. 
Polarizing filters remove light with a certain polarity to reduce or increase glare, particularly from window reflections or water.
Neutral Density filters reduce light without changing the color.
Color filters remove light of a particular color.
There are special filters that must be used with film that is sensible to infrared light.
So called diopters or close-up lenses make the image bigger. They are a cheaper way to do macro photography
A diffusion filter shows a subject softer, by adding some 'fuzziness'; this can be wanted in some cases, usually portraits of a person.

Filters can be cheap or expensive. Glass (or plastic) that is treated or coated in different ways usually costs more. Some filters can be screwed in front of a lens that is made for this. Others can be placed in the back of the lens, or in special filter holders screwed in at the front.

References

Category:Photography