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Hyperfocal Hocus Pocus

This past spring, I covered the basics of depth-of-field and the use of the DOF Preview button, but there is a related topic I haven't touched on yet: hyperfocal distance. Many photographers have heard of hyperfocal distance, but only some of them can say they honestly understand it.

We know that the depth-of-field describes the distance range within the frame that is in relative focus, both in front of and behind the point we are actually focused on. The near-focus distance is then the closest point that appears to be in focus, and the far-focus distance is the far end of the DOF range. If we focus the lens at or near infinity, we are therefore wasting the portion of the available DOF that extends beyond infinity (a strange concept, I admit, but this is really just another way to say that it is wasted). Instead, if we focus the lens such that the far-focus point is at infinity, the maximum range of distance is in focus and the lens is said to be focused on the hyperfocal distance.

So, the important question is, how do we do it?

Lens markings on a 50mm f/1.8 AFDOlder fixed focal-length lenses (and some current ones) have an aperture scale engraved on them next to the focus-distance scale. Some zoom lenses even have curved lines along their barrel that form an aperture scale for their focal length range. If you have a lens with a scale, you can use a simple procedure to focus at the hyperfocal distance. First, determine the aperture you will need to use for the shot you are trying to take. Then, examine the aperture marks on the DOF scale. Notice that the marks appear in pairs, left and right of a center mark. With a zoom lens, only pay attention to the scale at the focal length selected. Align the infinity mark with the left mark for the selected aperture and you're now focused at the hyperfocal distance (the center mark). The matching right mark for the aperture now points to the near-focus distance. Note that some lenses, both prime and zoom, only have a far-focus aperture mark — consult the documentation for your lens if you need help determining what marks, if any, you have to work with. Practice this technique at home, before you need to use it in the field.

What if you don't have any form of aperture marks to determine DOF? One solution is to use a chart such as the one below:

Feet f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 f/32
18 mm 15.0 10.6 7.5 5.3 3.8 2.7 1.9 1.3
24 mm 26.7 18.9 13.4 9.5 6.7 4.7 3.3 2.4
35 mm 56.9 40.2 28.4 20.1 14.2 10.1 7.1 5.0
50 mm 11.6 82.0 58.0 41.0 29.0 20.5 14.5 10.2
90 mm 376 266 188 133 94.0 66.4 47.0 33.2

For those interested in the details of how this was calculated, the formulas for hyperfocal distance are a bit complicated. The first thing you have to decide on is what value you are going to use for the circle of confusion. As a refresher, the COC is a measure of the size of circle that can not be distinguished from a point. Obviously, some people will be more picky than others, so there is some disagreement as to what value to use. The generally accepted values for 35mm film are between 0.025 and 0.030 mm. For the table above, I have used the bottom of this range in order to produce results that should satisfy everyone. Being smaller than 35mm film, focusing is more critical on digital cameras than it is on film, and the accepted values for circle of confusion are therefore less than what I've shown above. As an example, the Nikon DX sensor format requires a circle of confusion value more in the range of 0.02. If you are interested in the details of calculating DOF and hyperfocal distance, a great resource is this page.

Another solution is to use some software as a DOF calculator. DOFMaster from the page above is good, as is f/Calc. There's also a web page that will generate a custom hyperfocal chart you can print out and take with you.


Date posted: December 1, 2002 (updated October 15, 2004)

 

Copyright © 2002, 2004 Bob Johnson, Earthbound Light - all rights reserved.
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Previous tip: Getting to Digital One Step at a Time Return to archives menu Next tip: Petzl Headlamps

Related articles:
Depth of Field, Part 1
Hyperfocal Focusing with Digital: Because There's Not Much to See Beyond Infinity
 

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