An aperture is an opening in a lens through which light can pass. Apertures
are set at standardized intervals, referred to as f/stops. F/stops help control
image sharpness by partially correcting for lens aberrations and defining
depth of field. Changing aperture settings changes the amount of light
allowed to strike the film. The greater the numerical value of the f/stop, the
less light enters the lens. Each increment divides the light by half. If your
camera or hand-held meter is not working or you find yourself in a situation
where you havent the time to calculate an f/stop, use the f/16 rule; that is,
set the f/stop to f/16 and the shutter speed to the film speed, or as close to the
ISO that the shutter speed adjustment will allow.
Figure 4-19 shows standard f/stop increments.
Figure 4-19. Standard f/stop increments.
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