Knowing the underwater exposures and Filters

Underwater Exposures

Exposure settings for underwater photography depend on so many variable factors that it is hardly possible to make specific recommendations that will be generally useful. Among other considerations, the exposures in any situation will depend on weather conditions, the angle of the sun, the clarity of the water, the distance of the subject below the surface, and the color of the bottom. One do-it-yourself way to determine exposures is to seal a light meter in a waterproof jar and take it under for a reading; and there are a number of special “underwater” light meters, and housings are available for most standard light meters. As is so frequently the case in specialized applications of photography, it will be necessary to experiment to determine the best exposure settings for black-and-white and color films.

Underwater color photography presents a number of complex problems caused by the selective absorption and selective scattering of the different colors of light by water. The details will vary for different localities and for various water conditions, but in general red and blue wave lengths tend to be absorbed, so that the light that penetrates to any distance below the surface tends to be decidedly greenish.

Filters

Although daylight does penetrate water to a considerable depth, color absorption and scattering make effective use of natural light limited to the period between midmorning and early afternoon. For depths below 6 feet, it is usually helpful to use a filter to counteract the greenish tinge imparted by water.

For black-and-white film, a medium contrast filter generally gives better results. The Wratten is satisfactory for most waters and has about a 2-time factor or one stop when used with panchromatic black-and-white film. Excessive blues and greens have to be held back to allow reds, browns and yellows to receive their proper share in the color balance. With a filter, the maximum camera range through water is about 40 feet. The greater the distance through water, the more filtering is required, resulting in a denser filter to compensate. At present it appears that until faster color film is available, distances greater than approximately 40 feet through water are impractical to filter. The important fact to have in mind for using underwater color filters is the light distance through water. This involves both distance and depth. For example, if your depth is 5 feet and your object is 15 feet from the camera, your light distance through water is 20 feet.

An underwater color filter with a factor of approximately 2 times or one stop is effective up to about 20 feet through water. One with a factor of approximately 4 times, or 2 stops, is effective from about 20 feet to 40 feet. Those factors cover daylight-type color film. Distances beyond 40 feet will be aided considerably by the use of a filter, if light is sufficient to bring them in. It has been found that results are better if the background of the underwater picture is held to within 40 feet. In underwater photography it is important to “background” your photographs. Better results will be obtained if the subject is “shot” against coral or other background within the effective camera range. Do not shoot into a water mass.

Underwater filters are made of plastic and are moderately

Scuba equipment and the plastic-encased underwater camera have opened new vistas for amateur and professional photographers.

stable, but should be kept out of direct sunlight and covered when not in use. The filters can be used on underwater cameras with filter mounts on the outside. Wash them with fresh water after using. They are susceptible to scratches, but small scratches will not interfere when used under water on the outside of a camera case.

In discussing filters, it is necessary to speak in approximations in some cases. The use of filters under water (the same as in air) will vary with surrounding conditions. Under water, they are: turbidity, sunlight and clouds, and particularly the color of the water. The judgment gained by experience will be of value in selecting filters as well as other photographic settings.

For the ultratechnical expert, the underwater filter should be changed to a small degree according to the water color found in each location each day, and possibly each hour. However, for general use the filters described above should satisfactorily cover the greatest number of underwater situations.

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