Photographers talk a lot about depth of field, but few non-photographers really understand what it’s all about. In essence, depth of field refers to what’s in focus in front of and behind the subject you are shooting. With a little understanding, you can control what is in focus behind your subject. Why would you want to do this? Controlling your background’s focus can either help your subject stand out against a fussy background or can ensure that everything in that beautiful landscape shot is in focus.

The shot above was taken from the movie, Seabiscuit and is a great example of very shallow depth of field. You can see that only the horse and rider are in focus, while all the spectators in the foreground and background are out of focus.

There are two primary controllable factors that affect depth of field for digital cameras: lenses and f/stop. There are also ways to control depth of field in point-and-shoot cameras…

LENSES
The first controllable factor is your choice of lens. The longer the lens (more zoomed in you are), the less depth of field you will have. The wider the lens the more of your scene will be in focus. Above is an example of the same shot using different lenses. The top shot was made using a wide angle lens. You see a lot of the background and everything in the image is in focus. The bottom shot was made using a telephoto lens (long lens). You can see there is a narrower field of view for the background (meaning you don’t see as much on the right and left sides of the frame), and the grass behind the camera is out of focus. Simply moving your body farther away from the subject and zooming in allows the subject in the picture to pop out of the background. For more about lenses, click here.

F/STOP

If you have a Digital SLR camera that allows you to control your settings, there is a second factor that will affect your depth of field, called F/Stops. Every camera lens has an opening called an aperture that allows light to travel through the lens to the digital camera’s sensor (or to the film in a film camera).

F/Stop refers to settings for the aperture and determines the amount of light that is allowed through the lens. A wide open aperture (which has a lower number like f/2 or f/4) will diminish the depth of field. A more closed aperture (which has a higher number like f/16 or f/22) will increase the depth of field.

If you want the background of your shot to be very out of focus, choose a long lens and a wide aperture, such as f/4 (but don’t use the flash!). If you want everything you see to be in focus, choose a wide lens and shoot in bright light with a small aperture like f/22.

You might find yourself in a bright light situation but want to diminish your depth of field. There are three ways to do this. The first is to choose a very fast shutter speed, such as 1/1000 of a second and close down the lens for a small aperture. Another way to do this is to use ND filters. ND means Neutral Density filter, and it cuts down the light traveling through the lens so you can “stop down,” open your aperture to diminish your depth of field. Finally, you can change your ISO setting to 50ASA or even slower if you have that option on your camera.

POINT-AND-SHOOT DEPTH OF FIELD

But what do you do if you’re a point-and-shoot user? Well, there are ways to manipulate depth of field with these cameras as well. The Landscape setting is the perfect setting if you want maximum depth of field. The camera automatically chooses a more closed f/stop for maximum focus when set to the landscape setting.

If you want shallower depth of field (to have the background more blurry), choose the portrait setting. The camera automatically chooses a more open f/stop in portrait mode to make your subject pop out of a blurry background.

For more information, read the definition of depth-of-field in Wikipedia.

Stay tuned to next week for a feature about hyperfocal distance.