Exposure Compensation Using The Zone System
An early application of exposure compensation was the Zone System developed by Ansel Adams and Fred Archer. Although the Zone System has sometimes been regarded as complex, the basic concept is quite simple: render dark objects as dark and light objects as light, according to the photographer's visualization. Developed for black-and-white film, the Zone System divided luminance into 11 zones, with Zone 0 representing pure black and Zone X representing pure white. The meter indication would place whatever was metered on Zone V, a medium gray. The tonal range of color negative film is slightly less than that of black-and-white film, and the tonal range of color reversal film and digital sensors even less; accordingly, there are fewer zones between pure black and pure white. The meter indication, however, remains Zone V.
The relationship between exposure compensation and exposure zones is straightforward: an exposure compensation of one EV is equal to a change of one zone; thus exposure compensation of −1 EV is equivalent to placement on Zone IV, and exposure compensation of +2 EV is equivalent to placement on Zone VII.
The Zone System is a very specialized form of exposure compensation, and is used most effectively when metering individual scene elements, such as a sunlit rock or the bark of a tree in shade. Many cameras incorporate narrow-angle spot meters to facilitate such measurements. Because of the limited tonal range, an exposure compensation range of ±2 EV is often sufficient for using the Zone System with color film and digital sensors.
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