Aperture settings (f/stops) regulate the intensity of light allowed to strike the
film surface. The aperture control ring on the lens barrel is marked in a
series of f/stops that relate to the openings of the iris diaphragm.
control overall image sharpness, depth of field, and partially correct lens
aberrations. Adjacent numbers in the series of f/stops admit light in a
proportion of 2 to 1.
For example, changing aperture setting from f/5.6 to
f/8 changes the amount of light by decreasing the light by half, a procedure
called stopping down. Changing from f/5.6 to f/4 doubles the light. This
change is called opening up. When the diaphragm is set to its smallest
numerical aperture, it is said to be wide open. The larger the f/stop numbers,
the smaller the opening and the less light admitted.
Figure 7-16 illustrates the differences between f/stop openings.
Figure 7-16.Aperture: A. Aperture ring; B.
Aperture openings at various f/stops.
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