Lenses, ContinuedLens aperturesAperture openings are located on a ring or collar around the lens barrel. Thesize 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 fieldDepth of field is the distance from the nearest point of acceptably sharp focusto the farthest point of acceptably sharp focus.Depth of field depends on thefocal length of the lens, the f/stop setting, and the distance at which the lensis focused. Depth of field is greater with short-focal-length lenses than withlong-focal-length lenses. As aperture decreases, depth of field increases. Itis more important to focus accurately on nearby objects than for distanceobjects. When you want maximum depth of field, focus the lens on thehyperfocal distance or infinity for the f/stop used, not on the subject.Topreview depth of field before exposure, depress the preview button orpartially depress the shutter release to stop down the aperture.An estimateof depth of field is shown on the aperature ring on most cameras.The ringshows an approximate range for depth of field.Figure 7-20 shows depth of field.Figure 7-20.—Depth of field.Continued on next page7-32
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