Lens Aperture

The aperture of the lens opening, which is controlled by the diaphragm, is given by a value called f-stop, which is defined as lens opening diameter divided by lens focal length. F-stop is thus a fraction. On most cameras, f-stop values are arranged in sequence, such that each interval represents a doubling (or halving) of light values. Smaller f-stop denominator values mean more light enters the camera; larger values indicate less light. The typical sequence of f-stops is given below (Shaw, 1994). Most lenses operate in the range f/2.8—f/22.

f/1, f/1.4, f/2, f/2.8, f/4, f/ 5.6, f/8, f/11, f/16, f/22, f/32

Although the f-stop values as fractions are useful as a comparable aperture definition for lenses of all sizes, the absolute amount of light entering the camera is still dependent on the lens diameter. Smaller lens diameters—as used in compact cameras in contrast to SLRs—allow fewer photons to reach the image plane during a given exposure time. For digital cameras, this in turn means higher image noise (Clark, 2008b).

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