Tuesday, September 13, 2011

Three Things that Control Depth of Field

Tamron recently posted on its blog a useful little article by Andre Costantini, titled Achieving that Selective Focus.

The posting reminds us that there are three things affecting the depth of field in our images. They are
  • aperture or f-stop
  • focal length
  • the distance to the subject
These three factors work together to affect the ultimate DOF outcome in the image.  At the same distance and aperture, a long focal lenth lens will have less DOF than a wide angle lens.  Getting closer to the subject will accentuate the blurring of the background, shortening the DOF, regardless of the focal length of the lens.  This works even with wide angle lenses.  A close shot using a 24mm lens at a distance of 7 inches will definitely blurr the distant background when shooting at f/2.8.  But stepping back a few feet, almost everything will be in focus at the same aperture.  The longer the focal lenth, the more pronounced is this effect of blurred background.

Constantini writes, "Wider apertures like f2.8 or f2.0 let in more light but provide less depth of field. With longer telephoto lenses there is less depth of field. And the closer your focusing point, or to generalize the closer the subject to the lens, the less of your image will be in focus. This becomes especially apparent with true macro photography. So combining all of these principles will then create the most exaggerated effect."

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