Zone system

In photography, the zone system is a technique invented by Ansel Adams and Fred Archer in 1939 or 1940. It is one of the earliest methods to give photographers systematic control of their images by precisely defining the relationships between their equipment and materials.

Film

Monochrome (black and white) film can record a light intensity range of about seven zones. The luminosity range available within a scene, however, from the darkest shadows to the brightest areas, may be substantially larger or smaller than seven zones. Thus information can be lost in contrasty scenes due to the limited sensitivity range of film, or the range of film can be under-utilized in flat scenes.

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The zone system manages this by:

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• identifying what the film will record at different levels of exposure to the scene;
• processing the film in ways that modify the sensitivity range it ultimately records.

The objective is to preserve and render detail the photographer feels esthetically important.

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Ansel Adams' famous book The Negative lays out preliminary calibration and darkroom tasks, taking test pictures of the gray card at different exposures, simulating the zones, and then developing the film. Following his directions will bring to light any miscalibration of equipment and variations of developer chemistry due to the local water supply. Once completed, the photographer will have correctly calibrated equipment and a solid understanding of the zones.

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Development can be expanded (underexposed and overdeveloped) or contracted (overexposed and underdeveloped). This has the effect of expanding or contracting the contrast range recorded on the film, and can be applied to scenes that have a luminosity range unequal to the dynamic range of the film. Expansion and contraction also affects the contrast of the final image, and the zone system helps the photographer to have full control over these techniques.

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Color film has less range than monochrome, and sensors in digital cameras even less (although digital hardware is quickly improving). Some principles of the zone system, however, can be applied to color photography, largely in the area of light measurement and knowing what one can expect from color materials.

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