Depth of Field

Much like lens strength, subject distance, plays a big part in determining the possible size of depth of field. The closer you are to your focal point, or subject, the less depth of field is possible. To illustrate this effect, hold your hand at arm's length in front of your face. Even when focusing on your hand you can probably see a good bit of the surrounding environment in reasonably clear focus. Slowly move your hand towards your face until you reach the half-way point. Notice how much less of the area surrounding your hand is in focus. Continue moving your hand towards your face until it is as close as your eyes can focus on it. Very little of the area surrounding your hand can now be seen.

This same effect occurs with your camera lens. This effect, combined with high magnification factors, results in the tiny depth of fields seen in macro photography. It also makes the huge depths of field in many expansive landscapes possible when using a lower magnification factor lens.