A depth of field scale is a set of markings on the barrel of some lenses, usually manual-focus lenses. Pairs of aperture numbers sit on both sides of the focus mark. They show the nearest and farthest distances that will look sharp at a given aperture and focus setting.
You can use the scale to place the zone of sharpness exactly where you need it. This is useful for zone focusing and for setting the hyperfocal distance. The size of the sharp zone depends mainly on the aperture, focal length and focus distance.
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