UNDERSTANDING AND USING DEPTH OF FIELD

by Bill Popejoy April, 2004

What is Depth of field? It is the ZONE OF ACCEPTABLE SHARP FOCUS in a photograph. Three things determine Depth of Field:

(1) The distance that you focus on from the camera, FOCUS POINT.

The closer to the camera the focus point is, the less is the depth of field.

The farther away the focus point is, the greater is the depth of field.

(2) The focal length of the lens, FOCAL LENGTH.

The shorter the focal length is, the greater is the depth of field.

The longer the focal length is, the less is the depth of field.

(3) F Stop Numbers.

The smaller the F-STOP number is, the smaller is the depth of field.

The greater the F-STOP number is, the greater is the depth of field.

Depth of field and FOCUS POINT.

In general about one third of the depth of field is in front of the focus point and two thirds is behind the focus point.

USING WHAT WE KNOW ABOUT DEPTH OF FIELD:

For maximum depth of field, use the smallest F Stop number possible (Use Aperture Preferred), and/or use a short focal length and/or have the subject being photographed far from the camera.

For minimum depth of field, use the largest F Stop number possible, and/or use a long focal length and/or place the subject being photographed close to the camera.

Film comes in 50, 100, 200, 400 and 800 speeds. Using a “faster” film (larger number) allows one to use small F-Stops. Most digital cameras allow one to choose the “ISO” number in much the same way. You can choose any of the above numbers to achieve the same purpose. You can even change these numbers anytime, even after the last shot taken.

“Focus lock” allows one to focus anywhere in the frame thus controlling FOCUS POINT.

Cameras with “Zoom Lenses” allow one to choose the focal length being used.