Dave's Favorites: ExpoAperture Depth of Field Guide

Most digital SLR cameras--like the Canon Digital Rebel and the Nikon D70--feature a button that lets you see the effect of depth of field in the lens before you take the picture. That's an important feature if you want to be sure that only certain parts of the picture are in sharp focus while others are blurred and indistinct.

Expodisc now sells a handy little tool for calculating depth of field before you even pick up the camera. The ExpoAperture Depth of Field Guide is a pocket-sized, laminated disc with a rotating inner wheel. By spinning the two circles to line up distances, aperture (f/stop) numbers, and your camera lens focal length, you can answer questions like "what aperture do I need to set for 10 feet of focus," and "what will the depth of field be at an aperture of f/11?"

At first blush, the ExpoAperture looks complicated. It's full of numbers and wheels that spin and is populated with tick marks and data on both sides. But a no-nonsense user guide uses practical examples to teach you everything you need to know inside of 10 minutes--it's that easy.

If you have a digital SLR and obsess about the composition of your photos, the ExpoAperture Depth of Field Guide is $20 well spent. If you have a point-and-shoot digital camera, though, this is not for you: It's calibrated for lenses with true focal lengths that range from 18mm to 400mm.