I'd like a clear & easy-to-understand (especially for non-physics-types) explanation of what Hyperfocal Distance is, how it affects photographs, and what determines its value.
The hyperfocal distance is the distance at which everything from 1/2 the distance to infinity is in focus.
For instance, if the hyperfocal distance of a particular lens at a particular aperture is 100ft, then by focusing at 100 ft you can capture anything from 50ft-infinity in clear focus.
A more in depth explanation can be found at www.dofmaster.com
It's arguable whether this is "clear and easy to understand", but Thom Hogan has an interesting article on Hyperfocal distance - explaining that it's not quite what people think it is, and also why it's not necessarily a desirable effect.
Here's a few quotes (emphasis mine):
"Hyperfocal focus distance" is basically the focus distance for any given camera, lens, and settings that maximizes the apparent focus distance while including infinity at the far end.
Since a lens can only focus one distance at a time, hyperfocal focus depends upon the blur circle that is created by things in front or behind the focus distance to be small enough that we still detect it as a "point."
hyperfocal is really only usable for wide angle lenses. By the time you get to a 50mm lens, hyperfocal at f/11 is pretty much out beyond all the focus markings on the lens. I doubt that you'll be able to focus precisely enough to use even a rough hyperfocal number with that much lens
Hyperfocal focus done right looks wrong. It's an artificial construct promulagated by us photo writers who ran out of things to write about and started inventing things that seem useful but really aren't.
Our brains don't do "hyperfocal." Indeed, a critical depth cue our brain uses is that detail = near, lack of detail = far.
To determine the hyperfocal distance, you can use WolframAlpha's formula, it requires 3 variables:
- Circle of Confusion (CoC) in mm
- Focal length in mm
- Aperture (f-number)
The aforementioned DOFMaster site has a table with the different CoC values for various digital cameras.
Found this answer on dofmaster.com, which in turn references "How to Use Your Camera, New York Institute of Photography, 2000":
... the hyperfocal distance setting ... is simply a fancy term that means the distance setting at any aperture that produces the greatest depth of field.
Hyperfocal distance is the distance you focus to in order for the depth of field to extend backward precisely to infinity, representing the maximum depth of field in terms of focal distances covered.
Understanding this requires understanding what depth of field is.
Depth of field refers to the range of distances between which anything looks in focus. A wide depth of field means that subjects within a wide range of distances from the camera will look in focus, and a narrow depth of field means only subjects within a very narrow range of distances will appear in focus.
Technically, there is always only a single focal distance, but the nature of image sharpness means there is some tolerance either side of this before which you can tell a subject is out of focus. This tolerance varies according to various properties of the lens including its aperture size.
On lenses with mechanical focus rings (often older lenses), there are often depth of field markers showing you the near and far depth of field limits for each aperture. It extends each side of your actual focal setting. If you don't have these markers you can still work out depth of field mathematically or by an educated guess.
For any given aperture, you can turn the focus knob until the far limit of your depth of field sits exactly at infinity. The hyperfocal distance is whatever distance you need to focus to in order to achieve this. It'll be different according to your aperture.
Everything between half your hyperfocal distance and infinity will then be within your depth of field.