Filters for Color

Recording color involves greater knowledge about light sources than is necessary for black & white imaging. Sunlight, daylight and exterior lighting at different times of day,as well as incandescent, fluorescent, and other artificial sources, all have color characteristics that vary significantly. We see images through our eyes only after they are processed by our brain, which has the ability to make certain adjustments to the way we see color. White will still appear white to the eye in various lighting situtations, as long as we don't have more than one type visible at a time. Film has no such internal compensation. It is designed to see only a certain type of light as white — all others will appear different to the extent of their difference. Filters are required to provide the necessary fine-tuning.

The following discussion of Color Conversion, Light Balancing, Color Compensating, Decamired, and Fluorescent filters will be better understood after consulting the section on color temperature and light-source characteristics.

Color-conversion Filters

Color-conversion filters are used to correct for sizable differences in color temperature between the film and the light source. These include both the Wratten #80 (blue) and the Wratten #85 (amber) series of filters. Since they see frequent outdoor use, in bright sunlight, the #85 series, espe-

Graduated Color Filter

dally the #85 and #85B, are also available in combination with various neutral- density filters for exposure control.

Light-balancing Filters

Light-balancing filters are used to make minor corrections in color temperature. These are comprised of both the Wratten #81 (yellowish) and the Wratten #82 (bluish) series of filters. They are often used in combination with color-conversion filters. Certain #81 series filters may also be available in combination with various neutral density filters for exposure control.

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Sepia Filter

Color-compensating Filters

Color-compensating filters are used to make adjustments to the red, blue or green characteristics of light. These find applications in correcting for color balance, light source variations, different reversal film batches, and other color effects. They are available in density variations of Cyan, Magenta, Yellow, as well as Red, Blue, and Green filters.

Decamired Filters

Decamired filters (a trademark of their manufacturer) are designed to more easily handle unusual color tempera-

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Split-Field Lens ture variations than previously mentioned filters. Available in incremental mired shifts (see lighting section on mireds) in both a red and a blue series, decamired filters can be readily combined to create almost any required correction.

Fluorescent and Other Discontinuous Spectra Lighting Correction

Since filters never actually add color, but only absorb certain wavelengths to increase the relative proportion of others, the original light source must include the colors you want. Some sources are totally deficient in certain wave

lengths, which filters alone cannot add back. This is particularly true of many types of metal halide lighting. With other lighting types, such as fluorescent, color temperature measurements may not provide the correct filter requirements since color temperature theory is based on having a continuous spectrum, meaning light at all wavelengths. It is possible for a light source to have a sufficient spectral distribution to emulate a correctable color temperature when so measured, but its effect on film can be very different. (See section on lighting for additional details.)

Gradated Color Filters, or Wedges

Similar to Gradated ND filters, these filters are also produced in a wide range of standard and custom colors, densities, and proportions for many applications. A blue-to-clear filter can add blue to a white, hazy sky without affecting the foreground. An orange-to-clear filter can enliven a tepid sunset. Color can be added to the bottom of the scene, as with a green-to-clear filter used to enrich the appearance of a lawn.

Stripe filters are another type of gradated filter, having a thin stripe of color or neutral density running through the center of the filter, gradating to clear on either side. These are used to horizontally paint various colors in layers into a sky, as well as for narrow-area light balancing.

Coral Filters

As the sun moves through the sky, the color temperature of its light changes. It is often necessary to compensate for this in a variety of small steps as the day progresses, to match the appearance of different adjacent sequences to look as if they all took place at the same time. Coral filters include a range of graded filters of a color similar to an 85 conversion filter. From light to heavy, any effect from basic correction to warmer or cooler than "normal" is possible. Corals can also compensate for the overly cool blue effect of outdoor shade.

Sepia Filters

People often associate sepia-toned images with "early times." This makes sepia filters useful tools for producing believable flashbacks and for period effects with color film. Other colors are still visible, which is different from origi nal sepia-toned photography, but these colors appear to be infused with an overall sepia tint.

Didymium Filters

This type of filter, which may be called by a trade name (see manufacturers), is a combination of rare earth elements in glass. It completely removes a portion of the spectrum in the orange region. The effect is to increase the color saturation intensity of certain brown, orange, and reddish objects by eliminating the muddy tones and maximizing the crimson and scarlet components. Its most frequent use is for obtaining strongly saturated fall foliage. The effect is minimal on objects of other colors. Skin tones might be overly warm. Even after color timing to correct for any unwanted bias in these other areas, the effect on reddish objects will still be apparent.

Underwater Color-correction Filters

When filming underwater, the light you are recording is filtered by the water it passes through. Longer-wavelength reds and oranges are absorbed luitil only blue is left. The actual effect is determined by numerous factors, such as light source (sun or artificial), water quality, and the water path. The latter is the distance the light travels through the water. In natural (sun)light, this is the depth of the subject from the surface plus the subject-to-camera distance. For artificial lighting, it is the distance from the light to the subject to the camera. The longer the water path, the greater the filtering effect of the water. In many cases, certain color-compensating (CC) filters can absorb enough shorter wavelengths to restore better color balance. The difference between corrected and uncorrected color can be dramatic. The use of faster-speed films will facilitate the use of light absorbing correcting filters.

Differences Between Camera and Lab Correction

It is the job of the lab timer to fine-tune the finished color rendition of the film. This accounts for variables in exposure, print stock and processing. Timing can also be used to impart certain color effects, both for standard correction and special situations. The difference is that lab correction has only the range of colors and densities available in the film emulsion to work with, and is limited to the range of variation of the printer. These are much more limiting than the multitude of colorants in the real world, and the number of ways in which adjustments can be made at the camera. Filtering on the camera brings the lab that much closer to the desired result, providing a greater latitude of timing options.

There will be times when counting on the lab is the only choice. Labs can also produce some unusual effects. When faced with a low-light situation, in daylight using tungsten film, it may be necessary for exposure reasons to pull the 85 filter and correct in the printing. When you do this, however, neutral gray tones will appear slightly yellow, even when all else looks correct. This effect can be used to artificially enhance lush green foliage colors through the addition of yellow. It may have other vises, but you will not achieve the same result as if you had used the 85 filter.

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