A spot meter measures the light from a very small part of the scene. In a camera, spot metering usually reads about 1 to 5 percent of the frame, either in the center or at the active focus point. Handheld spot meters often measure an area of only 1 degree.
Spot metering is useful when the subject is much brighter or darker than its surroundings, for example a lit face on a stage. It is also a key tool in the Zone System. Compare evaluative metering and centre-weighted metering.
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