Depth of field is the distance range within which objects in a picture look sharp. As you gain a sound understanding of depth of field, you can use it as a very effective control for making better pictures.

What are the primary factors affecting depth of field? Depth of field varies with the size of the lens opening, the distance of the subject focused upon, and the focal length of the lens. Depth of field becomes greater as

1. the size of the lens opening decreases, the subject distance increases.
2. the focal length of the lens decreases.
3. and subject distance remains unchanged.

Three factors affecting depth of field.

An object at the distance focused upon will be the sharpest thing in the picture. But image sharpness doesn't suddenly disappear at the limits shown. Points closer or farther away than the distance focused upon will be less sharp, but will look acceptably sharp to the eye throughout the depth-of-field zone. Objects close to the depth-of-field zone may appear almost sharp. But the farther an object is from this zone, the more out of focus it will appear. In looking over these illustrations you can see that there are times when accurate focusing is very important because depth of field is slight. These include times when you're using a long-focal- length lens or a large lens opening or when you are close to your subject. Of course, a combination of these factors makes accurate focusing even more important. For example, let's assume you're using a 135 mm telephoto lens on your camera. If you're focused on a subject 14 feet away with a lens opening of f/4, your depth of field will extend from about 13 1/2 feet to 14 1/2 feet. This doesn't allow much room for focusing error!

You can use depth of field as a control in your pictures. In some shots you'll want as much depth of field as possible. For example, in shooting a scenic picture you may want to include tree branches in the foreground as an interesting frame. To get both the branches and the distant scene in sharp focus, you may use a wide-angle lens and a small lens opening for great depth of field.


As this series shows, using a smaller aperture (larger f-number) increases the front-back sharpness (depth of field) in a picture. In the first picture, taken at f/2, only the foreground rock is sharp. In the last picture, taken at f/16, the whole picture is sharp from front to back.

In other situations you may not want so much depth of field. You may be photographing a very interesting subject. But what if the background is confusing? You can use a large lens opening, perhaps combined with a long focal-length lens, to produce shallow depth of field. The disturbing background will be out of focus so as not to detract from your subject. The shallow depth of field will help focus attention on the main subject.

You'll probably want to have the foreground objects in sharp focus in most of your pictures. But you may want to make exceptions now and then to produce creative results. Sometimes an out-of-focus foreground can add interest, excitement, color, glamour, and intrigue to your photograph.

If you are using a manual-exposure camera, selecting the proper aperture for creative depth of field control is easy. Most auto-exposure cameras also provide a means to manipulate the aperture/shutter-speed combination to achieve maximum or minimum depth of field. There are several options for accomplishing this.

To achieve extensive depth of field, for instance, some automatic cameras have a special depth-of-field program mode. Once set to this mode, the camera will select a shutter speed and aperture combination that gives priority to choosing the smallest possible aperture. Similarly, many auto-exposure cameras have an aperture- priority mode that enables you to control depth by allowing you to set the specific shooting aperture. Choose a large aperture such as f/2.8 for shallow depth; or a small one such as f/11 for more depth. The camera will then choose a corresponding shutter speed for correct exposure. Or, if your auto camera allows, you can switch it to full manual and use it as a manual camera.

Depth-of Field/ Hyperfocal Distance

What part of the scene will fall within the depth of field? You can find out by using the depth-of-field scale on your lens. If there's none on the camera or lens, see the depth-of-field tables in your camera or lens instruction manual.

The lens depth-of-field scale not only helps you put the depth of field where you want it but also helps you get the amount of depth of field you want (see illustration). If you're taking a scenic picture, for example, you'll probably want all the depth of field you can get. If you simply focus on the distant scene, you'll be focused on infinity. But that's wasting a lot of depth of field. To have the most distant object in focus and also as much foreground as possible in focus as well, you can use a technique based on the hyperfocal distance.

To figure the hyperfocal distance, first set your lens to infinity. Then use the depth-of-field scale to read the nearest distance that will be in sharp focus at the aperture you are using. When you focus a lens on infinity, the near distance beyond which all objects are in acceptably sharp focus is the hyperfocal distance. For example, with a 50 mm lens set at f/16 and focused on infinity, the near-limit indicator on the depth-of-field scale shows that all objects from 15 feet to infinity will look sharp. The hyperfocal distance is 15 feet.

If you now refocus the lens to the hyperfocal distance (by setting the hyperfocal distance across from the focusing index), 15 feet in this example, objects from half the hyperfocal distance, 7 1/2 feet, to infinity will appear in sharp focus. (See illustration.) Using the hyperfocal distance will always give you the greatest depth of field for that particular lens opening. As you open the lens aperture to larger openings, the hyperfocal distances get farther away and the depth of field decreases.

With an auto-focus camera, you can either use the aperture that the camera has selected, or use an aperture-priority or full-manual exposure mode so that you can select a specific working aperture. Then with your lens focused on infinity, read the hyperfocal distance from the depth-of-field scale. Finally, switch your lens to manual focus and set it for the hyperfocal distance. Not all autofocus cameras have a depth-of-field scale or allow manual focusing.

Very often it's beneficial to know what distance to focus your camera on to get everything sharp within a range of medium distances. This is especially helpful when you're taking pictures rapidly without enough time to consult the depth-of-field scale or if there is no such scale on your lens. As a general rule, approximately 1/3 of the depth of field is in front of the point of sharpest focus with 2/3 of the depth of field behind. As a result, you should focus on a distance 1/3 of the way from the nearest object you want sharp to the farthest. For example, for objects within a 5-to 20-foot range, you should focus on 10 feet and use the smallest lens opening that you can. This rule does not apply to very close subjects or to those at great distances from the camera, including those at infinity.