Depth-of-field is the most misunderstood, most ignored technique that can turn a snap into a photograph. Exposure can be left to the camera, but to take charge of depth-of-field requires a traditional photographic technique irrespective of camera.

When the photographer focuses on a subject, part of the image in front of and behind the subject will also be in focus. But working out how much is not easy. It is dependent on aperture, focal length of lens, distance between photographer and subject and the physical size of sensor. Regardless of how these parameters are set the ratio is always the same - 1/3rd in front of the subject 2/3rds behind. Therefore if depth-of-field, as governed by the conditions above, turns out to be 6 inches in front of the subject, it will be 12 inches behind.

Using a small aperture (f22) will increase depth-of-field and additionally so does a wide-angle lens, but a large aperture (f2.8) and a telephoto optic does the opposite. Depth-of-field is also reduced the closer the photographer gets to the subject, especially less than 3 feet. Furthermore, the small sensors found in compact and bridge cameras seem to extend depth-of-field even further across the board, irrespective of other settings.

Because camera manufacturers cannot agree on the physical size, even shape, of the digital sensor, it is impossible to present a meaningful table; but an understanding of the basic concept of depth-of-field will assist many other aspects of photography, especially composition.