Aperture and shutter speed have a reciprocal relationship in making an exposure. Various different combinations of the two will produce the same exposure. The reciprocity law therefore means that an exposure provided by ƒ8 and 1/250 sec will gave the same results as ƒ11 and 1/125 sec., or ƒ16 and 1/60 sec., and so on. If one choice of settings provides proper exposure, then the others will as well. The reciprocity law states that Exposure = Intensity X Time. Intensity is the amount of light, and Time refers to how long that amount of light is allowed to act on the sensor or the film’s emulsion. The law fails, however, when slow shutter speeds change the film’s apparent speed characteristics, making it seem to have a slower speed and resulting in color shift.Photo Tips
Refers to the relationship between a camera s shutter speed and its aperture when taking a picture or making an exposure reading. Proper exposure of a subject will have a correct aperture that corresponds to a correct shutter speed. If you change either one, the other must change reciprocally to maintain correct exposure. Most cameras have the capability to automatically adjust one or the other setting when you make a change to either one. AS the aperture decreases, the shutter speed is slowed, and vice-versa.
When a film’s speed cannot be relied upon for proper exposure at slow shutter speed,reciprocity failure (or the Reciprocity effect ) is said to occur. Additional exposure is required in order to achieve proper exposure for that film, even though your light meter may say differently. The additional problem of a shift in color balance that occurs with reciprocity failure can be more troublesome.
Most films are designedto be exposed within a certain range of exposure times-usually between 1/15 secondto 1/1000 second. When exposure times fall outside of this range-becoming eithersignificantly longer or shorter-a film s characteristics may change. Loss of effectivefilm speed, contrast changes, and (with color films) color shifts are the three commonresults. These changes are called reciprocity effect. Generally, as a quick reference,exposure beyond one second needs to compensate for this characteristic of film.
A phenomenon that occurs when film is exposed under conditions that are not within its practical brightness range.
Expressed by (H)=Et, where E is the light intensity, and T is time. When E or T are varied to the extreme, an unsatisfactory exposure can result.