I. Focal length of the lens

The depth of field is inversely proportional to the focal length of the lens; that is, the smaller the focal length number of the lens, the greater the depth of field. For example, a 28mm lens has the ability to capture more of the picture in sharp focus than a 100mm lens.

II. Distance from the camera to the subject

Depth of field is directly proportional to distance; i.e. a subject at a greater distance will have greater depth of field than a close-up subject. Therefore, you need not worry as much about a distant subject being out of focus.

III. The size of the aperture or (f-stop)

While changing the aperture (f-stop) will not have a striking effect on the depth of field for a distant subject or a wide angle (short focal length) lens, it can make a great deal of difference in a close-up or a photo taken using a telephoto or zoom lens.

A wider aperture (smaller f-stop number) will result in a shallower depth of field. You can use this to keep either the foreground or background out of focus while maintaining the subject in focus. When changing the aperture setting, you will need to also adjust the shutter to maintain the correct exposure.

Aperture = F5.6 Shutter = 1/1000 Little/Shallow depth of field Aperture = F22 Shutter = 1/60 Greater/More depth of field