Reciprocity
Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.
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Famous quotes containing the word reciprocity:
“Between women love is contemplative; caresses are intended less to gain possession of the other than gradually to re-create the self through her; separateness is abolished, there is no struggle, no victory, no defeat; in exact reciprocity each is at once subject and object, sovereign and slave; duality become mutuality.”
—Simone De Beauvoir (1908–1986)