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SPECIAL-PURPOSE FILTERS Some of the special-purpose falters you will work with include the following: . Neutral density l Haze l Polarizing l Skylight Neutral density (ND) filters reduce the amount of light passing through a camera lens without changing the reproduction of colors in the scene. These filters are nonselective in their absorption of colors of light and therefore uniformly reduce the various colors of light in the spectrum. Thus white light and colored light are transmitted through a ND filter with only the intensity of the light being affected. These filters can be used with both black-and-white and color film. ND falters are gray in appearance. These falters may be needed for pictures of a brilliant subject in bright sunlight. When you have set the fastest shutter speed and the smallest f/stop and still cannot take the picture without overexposing the film, you can use a ND filter to further reduce the exposure. Haze Filters Suspended in the earth's atmosphere are minute particles of vapor and dust that cause a veil-like appearance called haze. This haze is most apparent in distant scenes. Haze is the result of sunlight being scattered by minute particles of matter that are present in the air. The amount of haze can vary due to atmospheric conditions. Haze should not be confused with mist, fog, smog, smoke or clouds. These conditions also can produce a veil-like appearance but falters have no effect. When sunlight is scattered, green and red light also are scattered by the ever-present haze, but not nearly as much as ultraviolet radiation, violet and blue light. Penetration of the haze is possible when filters are used to absorb scattered sunlight. A haze filter is any filter that absorbs atmospherically scattered sunlight. This includes contrast and correction filters. When contrast and correction filters are used for haze penetration, they may be considered special-purpose falters. Although contrast filters can be used for cutting haze, these filters affect the gray tone rendering of colored objects. The contrast and correction filters that absorb the shorter wavelengths are the most effective. The recommended contrast and correction filter colors, in the order of greatest to least effective, for haze penetration are as follows: l Red l Orange l Yellow l Green The use of an infrared sensitive black-and-white film with an infrared filter provides the greatest haze penetration of all. Polarizing filters look like gray neutral density filters. However, their effect becomes apparent when you look at the blue sky through a polarizing filter while rotating it. As you rotate the falter, the sky appears to get darker, then lighter. Polarizing filters are used in black-and-white and color photography for the following reasons: l To reduce or eliminate unwanted reflections (glare) from nonmetallic surfaces, such as glass and water l To effect exposure control (similar to ND filters) l To reduce the effects of haze l To darken the blue-sky image in both black-and-white and color photography l To increase color saturation in a color photograph without altering the hues of image colors There are a number of different polarizing filters. However, there are only two main types: one type fits over the camera lens, and the other is designed to be used over a light source. Since they do not affect color, polarizing filters and screens may be used for both black-and-white and color photography. Skylight Filter A skylight filter adds warmth to a scene recorded on color transparency film by absorbing ultraviolet radiation. It does this by reducing the bluish cast prevalent in distant scenes and in scenes photographed on heavily overcast days or in open shade. A skylight filter is light pink in color. |
 
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