Hyper Focal Distance
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Hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus.
There are two commonly used definitions of hyperfocal distance, leading to values that differ only slightly:
The first definition: the hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp; that is, the focus distance with the maximum depth of field. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.
The second definition: the hyperfocal distance is the distance beyond which all objects are acceptably sharp, for a lens focused at infinity.
Formulae:
H = [f^2]/[N c] + f
where
H is hyperfocal distance
f is focal length
N is f-number (f / D for aperture diameter D)
c is the circle of confusion limit (Each camera type has its own value of circle of confusion)
For any practical f-number, the focal length is insignificant in comparison with the first term, so that
H ~ [f^2][N c]
This term is mainly used in Landscape photography where we generally try to achieve maximum DOF (Depth of Field).
More Information :
http://en.wikipedia.org/wiki/Hyperfocal_distance
http://www.dofmaster.com/hyperfocal.html
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