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Opaque filter

Opaque filters, such as the Hoya R72, are used for infrared photography. Infrared film is sensitive not only to infrared radiation but also to ultraviolet rays and the shorter wavelengths of the visible spectrum. This filter achieves the most dramatic infrared effects by blocking all but the infrared radiation from reaching the lens. It passes only wavelengths above 720 nm. A second version, the Hoya R90, passes only wavelengths above 900 nm.

Opaque filters are often used to record the distribution of vegetation, for various types of detection, and in medical photography. In popular photography they are used, in conjunction with infrared film, to capture dramatic frost-like landscapes where vegetation is rendered almost pure white and skies are dark. Since they block all visible light from the lens, it is impossible to see through the viewfinder of an SLR once the filter is attached. It is therefore necessary to work with a tripod, compose the shot and attach the filter just prior to making an exposure.


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