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Atmospheric influences when photographing 1)Haze Not only the air molecules ( see Rayleigh distribution ), but water vapor, too, is responsible for the clouding-over of the atmosphere. However, water vapor absorbs red and infra-red light. A high level of air humidity also cuts out the blue of the sky. Air pollution from industrial plants and over big cities presents a special haze problem. Short-wave radiation, especially, is absorbed by exhaust fumes and dirt suppression of ultraviolet rays. Even visible short-wave radiation ( violet and blue )is lowered by industrial haze. The color trmperature con sink to as low as 4500 K. This fact requires flexibility in filter production, especially for color photography.
Fog and mist cannot be filtered as haze can since the high content of water vapor and the water droplets absorb heat radiation producing blue illumination. A red conversion filter is advisable here. Shots in fog and mist are particularily suited to color deviation effects using green to blue filters ( see black-and-whit filters 061 and 081 ). The shot is more expressive of mood and more realistic when these filters are used. It is to be noted that the size of water droplets can affect the color of the light. Here, too, nature is not fixed and 100% predictable. But precisely because of slight changes in its behavior, we are continually offered new impressions and motifs. The light in shade is always bluer than in the sun as the result of the high dispersion of short-wave light. An UV haze filter can remedy the situation or even better a KR 1,5 conversion filter (Skylight).In deep mountains in the mountains, a KR 3 may even be necessary. In forest shade, color cast changes from bluish-green to green. A magenta color correction filter M 10 should then be used.
Light on its way through the air is dispersed by the molecules of oxygen, nitrogen and other gases. The shorter the wave-length, the greater the obstacles for the respective light colors and the greater will be the dispersion. A certain proportion of light only reaches the eye indirectly via light dispersion. The image of the object is seen by the eye and the photo lens as blurred and unclear. Haze adds to the intensity of this effect. Rayleigh distribution leads to the use of red and infrared filters fosr long-distance shots since this light is hardly impeded by air molecules. Dispersed light is very important for outdoor shots and is also discussed in the sections Skylight/Daylight ( see Rayleigh distribution ). The dispersion of light in the air is what has the greatest influence on photography as it effects an appreciable change on sunlight. Dispersed light also occurs in cloudy, dirty water, milk appears white because of dispersed light. The phenomenon that milk seems bluish when dilluted has basically the same cause as for the blue of the sky. Tabacco smoke, too, demonstrates this effect clearly. For this reason, it is possible to penetrate a smoke-filled bar by means of a red filter. Light from the sun is partly
polarized on its way throgh the atmosphere. At right angles to she
sun, the polarizing effect is at its greatest. The degree of
polarization depends mainly on the state of the atmosphere. The
proportion of polarized light is greatest in pure air. Where there
is heavy air pollution, skylight polarization can disappear
completely.
Without the use of
With color film, the
The sea like areas of snow on a glacier reflects considerable amounts of ultraviolet light. Shots then often become bluish or bleached of color. It is absolutely necessary to use an ultraviolet haze filter or when the sun is at its zenith, a KR 1.5 skylight filter. A polarizing filter can also be very helpful as long as it cuts out ultraviolet radiation. The atmosphere's power of absorption sinks as air density decreases. Daylight as a rule becomes brighter, ultraviolet radiation greater, and increasingly shorter waves penetrate the atmospheric layer. Skylight becomes bluer and the amount of polarized light increases. Polarizer shots set at full elimination render the sky almost black. Mountain sun always requires a strong UV haze filter. At very great heights, a flourescence cut-out filter is advisable to avoid the danger of self-radiation from the lens.
1) "B+W-Filters and special effects attachments: their correct use for better photos and films" by Arnold Mellert u. Dietrich Oppitz, 1978, ISBN 3-7949-0319-6 (out-of-print), by courtesy of Fachverlags Schiele&Schön |
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