A Focus on Focus

Gene Bjerke
May 2004

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Lighting, composition and exposure are just a few of the variables you must control on a shoot. It requires a high degree of personal multi-tasking to shoot it right. It is tempting to just depend on your camera's automatics to simplify your life and, in many cases, they will do the job just fine. But by maintaining control of one or more of these details yourself, you can make a sort of magic happen. Take one of the most fundamentals for instance: focus.

Most autofocus systems work well for most scenes. The autofocus typically assume that the center of interest will dominate the center of the frame. This will be true most of the time, but what if you decide to put your main subject off center? You may find that the background is in sharp focus, but your subject is a little soft. The way to make sure your audience focuses on what you want is to make sure that what you want is what is in focus. This is as much a creative decision as anything else and machines are not good at creative decisions. People are.

The creative use of focus depends on being able to control what is and is not in focus. Part of creative focus control is in knowing what you want to be sharp and what you don't.

You can direct your viewer's attention by making the main subject the sharpest part of the frame, no matter where in the frame that subject appears. To get the widest creative range for your focus, open the iris (aperture) up to the widest f/stop (see the sidebar), use the shutter to adjust the exposure and zoom in on your subject. Now, adjust your focus manually. This is easier if you can find some part of the subject with definite edges. The eyes and eyelashes are the best places to focus if you are doing a close-up of a person. You can also use anything with fine details, such as hair or a definite pattern in clothing. Anything with texture is also a good candidate for focusing, just make sure it is part of where you want your viewer's attention.

When you zoom back out to frame your subject for the shoot, your subject will be sharp and the rest of the frame will vary depending on your depth of field. Usually, you'll want the foreground to be sharp and the background softer. Very short lenses, like those found on small consumer camcorders, have a deep depth of field, so your background may be as sharp as the foreground and compete with it for attention. One solution is to move your subject farther away from the background. Another is to zoom in, changing the lens to a longer focus. If these are not practical options, you can put the point of focus just far enough in front of your subject so that the background goes soft.

In some cases, you may want the opposite. Peering at your subject through some foreground object, such as leaves or flowers, can add a bit of mystery or atmosphere to a shot. This works best if the foreground object is out of focus and your subject, even if partly obscured, is sharp. This is strictly a manual-focus situation.

Video is a medium of motion. This sometimes means that the camera-to-subject distance changes during the shot, either because the subject or the camera is moving (or both). Even if the camera is not tracking backwards or forwards, you may pan or tilt on a scene that is at an angle to the camera, such as panning down a shelf of objects. In such cases, you may need to follow-focus, that is, adjust the focus as the shot progresses. At other times, you might want to change the focus in a static shot where neither the camera nor the subject is moving.

Since your viewers will watch the sharpest part of the frame, you can direct and move their attention for dramatic purposes without actually moving anything at all. A "rack focus" or a "shift focus" is one way to do this. As the names suggest, you shift the focus from one part of the frame to another. For example, your scene shows the heroine reading on a park bench. The sun is shining and life is peaceful. Then the focus shifts to the previously out of focus background to reveal the stalker, staring at her. The audience is immediately made aware of something the subject isn't aware of and proximity is established and even reinforced, since the two people are in the frame at the same time.