Depth of field. This is one of those terms that confuses new photographers. Once you get into lengthy technical explanations, it can confuse experienced photographers. But basically what it means is the range from foreground to background in which the elements of a photograph are in focus. You've probably seen portraits in which the person is sharply in focus, but the background is blurry. You can see this at work in Zoe's picture of the Squirrel or in Onions' picture of the Foxglove. You can also use it to interesting effect by bluring the foreground while focussing on the background, as in my picture Texas Spring. Or even blur both foreground and background, allowing only the middle range to be in focus. On the other hand, DOF also comes into play if you want all the elements of your picture to be in focus, as (for example) in a landscape.

So...how does depth of field work? Rather than get into a detailed technical explanation, let's get used to DOF first and just talk about some rules of thumb. (We'll save the really technical explanation for a later date.) First, remember when discussing aperture or f-stops, the smaller the number, the larger the opening (aperture). So at f/16 the camera opens the shutter less than at f/4.

Depth of field is governed by three factors: aperture, lens focal length and shooting distance.

1. The smaller the aperture, the deeper the depth of field (as long as the other two factors remain the same). For example, if the lens focal length and the shooting distance stay the same, the depth of field is much deeper at f/16 than at f/1.4



2. The shorter the lens focal length, the deeper the depth of field (again, as long as the other two factors remain the same). For example, comparing a 28mm lens with a 50mm lens at the same aperture and shooting distance, depth of field is deeper with the 28mm lens.



3. The greater the shooting distance, the deeper the depth of field (when the other two factors remain the same). For example, if the subject is photographed from three and then from seven meters away, the zone of sharpness in the foreground and background is greater at seven meters.

You should also know that lenses generally give their sharpest, best images near the middle range apertures (approximately f/8). So, also you might use f/16 to increase the depth of field, you may lose some quality of image sharpness. This is why professional photographers often have such a wide range of lenses. This doesn't mean you need to run out and start buying expensive, lenses to get good pictures, however. For most of us, the minimal loss of sharpness isn't noticeable enough to worry about.