Friday, October 10, 2008

Hyperfocus: Everything's clear now

TheGrove_Hyperfocus There's this interesting (and pretty cool-sounding) concept in photography called Hyperfocus. Hyperfocus is a physical property of a given lens which, when fixed at a certain focal point and set at a certain aperture, makes everything from half that distance to infinity appear in sharp focus! Too much to digest? Let's throw in some numbers to make it clearer. If I'm using a 50mm lens and I set the aperture to f/22, when I focus the lens to a distance of 20 feet, everything in the scene from 9'6" all the way to infinity will be in sharp focus. Sounds interesting? If you're a landscape photographer, it sure should.

Let's dig a little deeper. Lenses are strange and wonderful things--there so much of physics involved in them that its easy to get lost in those numbers if you look beneath the surface. Hyperfocus is one such concept that is deeply rooted in mathematics, and there's plenty of information out there if you're interested in digging deeper. But what's more practical are the actual settings for your camera and lens combination that result in a hyperfocal photo. Theoretically, you can set virtually any camera to hyperfocus--even your point-and-shoot digicam. All you need to know are the focal length, f-number, and the circle of confusion for your particular camera/lens combination. The first two parameters are straightforward, but what's this 'circle of confusion'? Basically, it's the smallest clear optical spot that a lens can make. So if you have a magnifying glass and you're focusing sunlight on a hapless crawling creature, the smallest spot you create (measured in mm) is the circle of confusion of that particular lens. In a digital camera, this spot is influenced by the lens and its optical characteristics. If you're interested in calculating the hyperfocal distance of your camera, use this equation here. But wait, there's a quicker way--generate a pre-defined chart of hyperfocus settings for your particular camera! The good folks at the dofmaster Web site have done all of the mathematical heavy lifting, and you can now create a custom hyperfocus chart for your camera model here. Simple.

Cameras don't have just one hyperfocal distance--this distance changes depending on the specific f-stop and lens focal length combination. This lets you select the best combination for your particular use. For example, the technique I find most convenient for hyperfocussing my D40 and its stock 18-55mm lens is:

  1. Set the zoom to 18mm.
  2. Set the aperture to f/16.
  3. Manually set the focus to 4 feet (I do this by holding my camera to my chest and auto-focusing on my shoes--I memorized the 4-foot mark. Then I set the lens to manual focus using the A/M switch.)
  4. Point the camera at the scenery and shoot!

I used the chart referenced earlier to figure out this set of hyperfocus settings. At these settings, everything from 1'10" in front of my camera to infinity is in sharp focus. Click the photo at that opening of this story to see what hyperfocus looks like. It's especially apparent when you have plenty of objects in the near and far field--all in sharp focus.


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