Understanding Depth Of Field

Making sense of the “circle of confusion".

- Seth Shostak

DEPENDING ON YOUR PHOTOGRAPHIC INTERESTS, depth of field—the range of distances over which your lens will be sharp—can affect you in either propitious or problematic ways. If you’re trying to isolate one face in a group, a shallow depth of field is just what you need. If you’re hoping to capture the drama of a racehorse beating down the track in your direction, then shallow depth of field can turn much of the equine into a befuddling brown blur, no matter how high your shutter speed.

Frankly, you don’t need to know the science that governs depth of field. You can rely on your preview button or those nifty white marks on your lens barrel. But then again, Napoleon ignored the logistics of marching into Russia, and the results were disappointing. It generally helps to understand what’s going on.

Depth of field is really based on a practical compromise. A perfect lens will bring everything at a given distance into sharp focus at the plane of your camera’s sensor. All subject matter either closer or farther will be unsharp. All of it.