Lenses, Continued
Lens apertures
Aperture openings are located on a ring or collar around the lens barrel. The
size of the largest opening, called the maximum working aperture of the lens,
is referred to as lens speed. Apertures also influence depth of field.
Depth of field
Depth of field is the distance from the nearest point of acceptably sharp focus
to the farthest point of acceptably sharp focus.
Depth of field depends on the
focal length of the lens, the f/stop setting, and the distance at which the lens
is focused. Depth of field is greater with short-focal-length lenses than with
long-focal-length lenses. As aperture decreases, depth of field increases. It
is more important to focus accurately on nearby objects than for distance
objects. When you want maximum depth of field, focus the lens on the
hyperfocal distance or infinity for the f/stop used, not on the subject.
To
preview depth of field before exposure, depress the preview button or
partially depress the shutter release to stop down the aperture.
An estimate
of depth of field is shown on the aperature ring on most cameras.
The ring
shows an approximate range for depth of field.
Figure 7-20 shows depth of field.
Figure 7-20.—Depth of field.
Continued on next page
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