Misplaced Pages

Hyperfocal distance: Difference between revisions

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
Browse history interactively← Previous editNext edit →Content deleted Content addedVisualWikitext
Revision as of 16:33, 7 March 2006 editDoug Pardee (talk | contribs)115 edits Clarification of the two meanings; added acceptable sharpness section← Previous edit Revision as of 22:47, 1 April 2006 edit undoDicklyon (talk | contribs)Autopatrolled, Extended confirmed users, Rollbackers477,152 edits Simplify to more commonly accepted viewpoint; simplify and clean up math and variable namesNext edit →
Line 1: Line 1:
'''Hyperfocal distance''' is a distance used in ] and ]. The precise value is slightly different between the two disciplines. '''Hyperfocal distance''' is a distance used in ] and particularly in ].


There are two commonly used definitions of hyperfocal distance, leading to values that differ only slightly.
In optics, when a ] 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 ]. 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 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 ]. 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.
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 distinction between the two meanings is rarely made, since they are interchangable and have almost identical values. The value computed according to the first definition exceeds that from the second by just one focal length.


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== ==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 ]. 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.). The hyperfocal distance is entirely dependent upon what level of sharpness is considered to be acceptable. The criterion for the desired acceptable sharpness is specified through the ] diameter limit. This criterion is the largest acceptable spot size diameter that an infinitesimal point is allowed to spread out to on the imaging medium (film, digital sensor, etc.).


==Formulae== ==Formulae==


The "optical" hyperfocal distance is the product of the square of the ] divided by both the ] and the ] limit chosen. The hyperfocal distance is the square of the ] divided by both the ] and the ] limit chosen.


:<math>H = \frac{F^2}{(f)(Cc)}</math> :<math>H = \frac{F^2}{N \cdot C}</math>


where where


:''H'' is "optical" hyperfocal distance :''H'' is hyperfocal distance


:''F'' is focal length :''F'' is focal length


:''N'' is f-number (<math>F/D</math> for aperture diameter <math>D</math>)
:''f'' is f-stop


:''Cc'' is the circle of confusion limit :''C'' is the circle of confusion limit


This formula is exact for the second definition, if H is measured from a thin lens, or from the front principal plane of a complex lens; it is also exact for the second definition if H is measured from a point that is one focal length lenght in front of the front principal plane. Another commonly used formula for the first definition is
The "photographic" hyperfocal distance is:


:<math>D = H+F \,</math> :<math>H = \frac{F^2}{N \cdot C} + F</math>


where

:''D'' is "photographic" hyperfocal distance

:''H'' is "optical" hyperfocal distance computed as above

:''F'' is focal length


==Examples== ==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: As an example, let's compute the hyperfocal distance for a 50 mm lens at <math>F/16</math> using a circle of confusion of 0.03 mm (which is a value typically used in 35mm photography):

⚫ :<math>H = \frac{(50 \mbox{ mm})^2}{(16)(0.02 \mbox{ mm})}</math>

:<math>H = \frac{(50 \mbox{ mm})(50 \mbox{ mm})}{(16)(0.02 \mbox{ mm})}</math>

:<math>H = 7812.5 \mbox{ mm} \,</math>

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

:<math>D = 7812.5 \mbox{ mm} + 50 \mbox{ mm} \,</math>

:<math>D = 7862.5 \mbox{ mm} \,</math>


⚫ :<math>H = \frac{(50 \mbox{ mm})^2}{(16)(0.03 \mbox{ mm})} = 5208 \mbox{ mm} \,</math>
⚫ If we focus the lens at a distance of 7.9&nbsp;m, then everything from half that distance (4&nbsp;m) to infinity will be acceptably sharp in our photograph.


⚫ If we focus the lens at a distance of 5.2&nbsp;m, then everything from half that distance (2.6&nbsp;m) to infinity will be acceptably sharp in our photograph. With the more exact formula for the first definition, the result <math>H = 5258 \mbox{ mm}</math> is not much different.
==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== ==External links==
*http://www.dofmaster.com/dofjs.html to calculate "photographic" hyperfocal distance and ] *http://www.dofmaster.com/dofjs.html to calculate hyperfocal distance and ]
*: real-world use for photographers, including its shortcomings and a hyperfocal chart calculator *: real-world use for photographers, including its shortcomings and a hyperfocal chart calculator


Revision as of 22:47, 1 April 2006

Hyperfocal distance is a distance used in optics and particularly in photography.

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.

The distinction between the two meanings is rarely made, since they are interchangable and have almost identical values. The value computed according to the first definition exceeds that from the second by just one focal length.


Acceptable Sharpness

The hyperfocal distance is 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 diameter limit. This criterion is the largest acceptable spot size diameter that an infinitesimal point is allowed to spread out to on the imaging medium (film, digital sensor, etc.).

Formulae

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

H = F 2 N ⋅ C {\displaystyle H={\frac {F^{2}}{N\cdot C}}}

where

H is hyperfocal distance
F is focal length
N is f-number ( F / D {\displaystyle F/D} for aperture diameter D {\displaystyle D} )
C is the circle of confusion limit

This formula is exact for the second definition, if H is measured from a thin lens, or from the front principal plane of a complex lens; it is also exact for the second definition if H is measured from a point that is one focal length lenght in front of the front principal plane. Another commonly used formula for the first definition is

H = F 2 N ⋅ C + F {\displaystyle H={\frac {F^{2}}{N\cdot C}}+F}


Examples

As an example, let's compute the hyperfocal distance for a 50 mm lens at F / 16 {\displaystyle F/16} using a circle of confusion of 0.03 mm (which is a value typically used in 35mm photography):

H = ( 50  mm ) 2 ( 16 ) ( 0.03  mm ) = 5208  mm {\displaystyle H={\frac {(50{\mbox{ mm}})^{2}}{(16)(0.03{\mbox{ mm}})}}=5208{\mbox{ mm}}\,}

If we focus the lens at a distance of 5.2 m, then everything from half that distance (2.6 m) to infinity will be acceptably sharp in our photograph. With the more exact formula for the first definition, the result H = 5258  mm {\displaystyle H=5258{\mbox{ mm}}} is not much different.


External links

Categories: