These are the main filters most commonly used in cinematography:
The Diffusion Filter diffuses light as it enters the lens, softening it. However, often it only appears to blur the light. Therefore, most cinematographers prefer to soften the light at its source, rather than as it enters the lens (see 'Gels').
The Polarizing Filter is used to control glare and reflection, for example, if you are filming through a window and need to keep the reflection of you and the camera from being seen in the shot. (This filter will also cut 2 stops of light from entering the lens.)
The Neutral Density Filter (ND) is used to cut down the amount of light that enters the lens, to reduce its intensity when it cannot be done from its source (such as a very bright sun). Often the filmmaker may wish to have a shallow depth of field, thus requiring an open aperture (a low number t-stop). This may require a reduction in the amount of light that enters the lens so as to keep from overexposing the film. NDs cut down light by 1/2, 1, 2, or 3 stops, depending on the particular ND (ND.15, ND.3, ND.6, ND.9).
Color Correction Filters are used to change the color temperature of the light as it enters the lens. They are generally either blue or orange/yellow and range in density depending on how "warm" or "cool" you want the light to be. However, for color contrasting, most DPs prefer to change the color at the source using gels. Color correction filters are most commonly used to balance the color, to make it white.
Learn more about color temperature, tungsten, HMI, and natural light, as well as the difference between film speeds and aspect ratios. Learn the proper use of filters and gels, the quality of different lenses, as well as tricks to reducing grain in 16mm blow ups to 35mm prints. Order "The Old School Film School" today.
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