Hyperfocal Distance
Definition: the smallest focusing distance of an imaging instruments for which objects at infinity appear with reasonably sharp focus
German: hyperfokale Entfernung
Categories: general optics, vision, displays and imaging
Author: Dr. Rüdiger Paschotta
Most imaging instruments can provide sharp images only in a limited range of observation distances, as explained in the article on depth of field. The minimum and maximum distance for reasonably sharp imaging both depend on the chosen focusing distance. If the focusing distance is gradually increased, it eventually reaches the hyperfocal distance, where the maximum distance becomes infinity. At this point, the depth of field reaches its maximum possible value for a given size of the aperture stop.
When focusing to infinity, distant objects will be imaged with somewhat better resolution. However, the minimum distance will then be substantially larger.
Some authors use a different definition for the hyperfocal distance: the distance beyond which all objects are reasonably sharp, when the objective is focused at infinity. In practice, this leads to about the same values as with the other definition.
See also: imaging, depth of field
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