Misplaced Pages

This is an old revision of this page, as edited by Doug Pardee (talk | contribs) at 16:33, 7 March 2006 (Clarification of the two meanings; added acceptable sharpness section). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Hyperfocal distance is a distance used in optics and photography. The precise value is slightly different between the two disciplines.

In optics, when a lens is focused at infinity, objects at the hyperfocal distance and beyond are acceptably sharp.

In photography, 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 "photographic" hyperfocal distance out to infinity will be acceptably sharp.

The distinction between the two meanings is rarely made; context is usually used to determine which meaning is intended. Since no accepted terminology exists for distinguishing between the two meanings, this article invents the terms "optical" and "photographic" hyperfocal distance. The modifiers are shown in quotes to emphasize that the terms are invented and not generally accepted.

The "photographic" hyperfocal distance is slightly greater than the "optical" hyperfocal distance. The difference between the two is the same as the focal length of the lens.

Acceptable Sharpness

The hyperfocal distances are entirely dependent upon what level of sharpness is considered to be acceptable. The criterion for the desired acceptable sharpness is specified through the circle of confusion. The circle of confusion is the largest acceptable spot size that an infinitesimal point is to spread out to on the imaging medium (film, digital sensor, etc.).

Formulae

The "optical" hyperfocal distance is the product of the square of the focal length divided by both the f-stop and the circle of confusion limit chosen.

${\displaystyle H={\frac {F^{2}}{(f)(Cc)}}}$

where

H is "optical" hyperfocal distance

F is focal length

f is f-stop

Cc is the circle of confusion limit

The "photographic" hyperfocal distance is:

${\displaystyle D=H+F\,}$

where

D is "photographic" hyperfocal distance

H is "optical" hyperfocal distance computed as above

F is focal length

Examples

As an example, let's compute the hyperfocal distances for a 50 mm lens at f/16 using a circle of confusion of 0.02 mm (which might be acceptable for some amount of enlargement). In the formula above, we make F = 50 mm, f = 16, and Cc = 0.02 mm; then we compute H:

${\displaystyle H={\frac {(50{\mbox{ mm}})^{2}}{(16)(0.02{\mbox{ mm}})}}}$

${\displaystyle H={\frac {(50{\mbox{ mm}})(50{\mbox{ mm}})}{(16)(0.02{\mbox{ mm}})}}}$

${\displaystyle H=7812.5{\mbox{ mm}}\,}$

The "optical" hyperfocal distance is about 7.8 m. To determine the "photographic" hyperfocal distance, we then compute D:

${\displaystyle D=7812.5{\mbox{ mm}}+50{\mbox{ mm}}\,}$

${\displaystyle D=7862.5{\mbox{ mm}}\,}$

If we focus the lens at a distance of 7.9 m, then everything from half that distance (4 m) to infinity will be acceptably sharp in our photograph.

Alternate usage

In informal usage, the focus point that allows a particular range of distances to be acceptably in focus at a particular aperture also is frequently called the hyperfocal distance. This is an extension of the concept of "photographic" hyperfocal distance to include depth of field ranges that do not extend to infinity.

External links

• http://www.dofmaster.com/dofjs.html to calculate "photographic" hyperfocal distance and depth of field
• Understanding Hyperfocal Distance and Charts: real-world use for photographers, including its shortcomings and a hyperfocal chart calculator

• Optics
• Length
• Photographic terms