depth of field
For a given setting of an optical system (or a steady state of accommodation of the eye) it is the distance over which an object may be moved without causing a sharpness reduction beyond a certain tolerable amount. Depth of field increases when the diaphragm (or pupil) diameter diminishes as, for example, in old eyes (Fig. D1). Examples: viewing at infinity, the depth of field ranges between infinity and about 3.6 m for a pupil of 4 mm in diameter; and between infinity and about 2.3 m for a 2 mm pupil. At a viewing distance of 1 m, the depth of field ranges from about 1.4 m to 80 cm with a 4 mm pupil; and from about 1.8 m to 70 cm with a 2 mm pupil. See hyperfocal distance.
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Fig. D1 Schematic representation of the depth of field and the depth of focus of an eye fixating an object at O (I, retinal image size corresponding to the tolerable resolution)
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