F/Stop System

In photography, a set of values used for setting camera lens apertures. Essentially, a specific f/stop (also called an f/number) is the ratio of the focal length of the lens to the diameter of the aperture. Thus, a camera (such as a procerss camera) with an 8-inch focal length and a 1-inch aperture diameter would have an f/number of f/8 (8 ÷ 1 = 8). Reducing the aperture to H inch would yield an f/number of f/16 (8 ÷ 1/2 = 16). Although in theory any f/number can be produced, lens manufacturers and photographers recognize a given set of f/stops: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, and f/64. The greater the f/number, the smaller the diameter of the aperture. Each f/stop also differs by a factor of 2 in the amount of light that is allowed to pass into the camera. Using f/stops, it is possible to gauge the exposure time required, and adjusting the lens aperture and f/stop can yield shorter (or longer) equivalent exposure times. (See Photography: Basic Photographic Principles.)

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