Aperture
Introduction
Aperture settings are related to and work in conjunction with shutter speeds.
Understanding the relationship between the two factors should improve your
ability to shoot correctly exposed films and papers with less effort.
Aperture
The aperture regulates the diameter of a lens opening.
The diameter of the
lens opening controls the amount of light or luminance that strikes the film
plane. Aperture is also referred to as f/stop. The term f/stop expresses the
relationship between the focal length of the lens and the diameter of the
aperture opening. The most commonly used aperture-control device is the
iris diaphragm.
Iris diaphragm
The iris diaphragm is an adjustable device that fits into the barrel of a lens or
shutter housing. It consists of a series of thin, curved, metal blades that
overlap each other and fasten to a control ring on the lens barrel. The blades
of the diaphragm move in unison as the control ring rotates, forming an
aperture opening of any size. An iris diaphragm resembles the iris in the
human eye; hence the name, iris diaphragm.
Figure 7-15 shows how similar the iris diaphragm is to the human eye.
Figure 7-15.—Iris and iris diaphragm under light:
A. Bright light; B. Low light.
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