Zone System

The Zone System is a photographic technique for determining optimal film exposure and development, formulated by Ansel Adams and Fred Archer. Adams described the Zone System as "[...] not an invention of mine; it is a codification of the principles of sensitometry, worked out by Fred Archer and myself at the Art Center School in Los Angeles, around 1939–40."

The technique is based on the late 19th century sensitometry studies of Hurter and Driffield. The Zone System provides photographers with a systematic method of precisely defining the relationship between the way they visualize the photographic subject and the final results. Although it originated with black-and-white sheet film, the Zone System is also applicable to roll film, both black-and-white and color, negative and reversal, and to digital photography.

An expressive image involves the arrangement and rendering of various scene elements according to the photographer’s desire. Achieving the desired image involves image management (placement of the camera, choice of lens, and possibly the use of camera movements) and control of image values. The Zone System is concerned with control of image values, ensuring that light and dark values are rendered as desired. Anticipation of the final result before making the exposure is known as visualization.

Any scene of photographic interest contains elements of different luminance; consequently, the “exposure” actually is many different exposures. The exposure time is the same for all elements, but the image illuminance varies with the luminance of each subject element.

Exposure is often determined using a reflected-lightexposure meter. The earliest meters measured overall average luminance; meter calibration was established to give satisfactory exposures for typical outdoor scenes. However, if the part of a scene that is metered includes large areas of unusually high or low reflectance, or unusually large areas of highlight or shadow, the “effective” average reflectance may differ substantially from that of a “typical” scene, and the rendering may not be as desired.

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