Making focus work to your advantage is a key part of producing good video.
One of the most common problems among video greenhorns is an inability to effectively control the camcorder's focus. Being able to control focus and, more importantly, making that ability work to your advantage is a skill that is key to your development as a videographer. Proper focusing techniques will ensure that your audience sees precisely what you want them to see at all times, while giving your video polish and style.
For example, you can manually manipulate your focus to shift from one subject to another, or to keep a moving subject in focus more effectively. You can even use focal effects as a transitional tool between shots.
How Your Camcorder Focuses
If you're like most casual shooters, you probably let your camcorder do most of your focusing for you. There's nothing wrong with that if you're willing to live with a drift in focus or the camera choosing to focus on the wrong part of your shot entirely, from time to time. But manual focus is required to achieve many particular focal effects, such as those mentioned above.
All camcorders are equipped with an autofocus feature. Autofocus uses electronics to determine when a subject is in focus and when it is not. You may not know that many camcorders allow you to override this feature and focus the camcorder manually. Look on your camcorder or check your owner's manual for specific details. In many cases you can toggle between automatic and manual focus with the press of a button located somewhere near your camcorder's lens. Some models may require you to select auto or manual through an internal menu setting.
Manually focusing the lens is generally pretty easy. Higher end camcorders may allow you to turn the lens's focus ring just as you would on a respectable 35mm still camera. Other camcorders may provide a small wheel on the outside of the camcorder which in turn manipulates the lens.
The trick here, however, is in knowing how much to manipulate the lens. Turn it too far and your subject goes out of focus. Turn it too fast and you'll probably find yourself overcompensating as you attempt to return focus to your shot. Adjusting manual focus while you are recording requires finesse. Simply remember to be gentle with the focus ring and you'll go a long way to controlling your camcorder's focus. Better still, adjust your focus before rolling tape and stop recording to reset your focal setting for the next shot.
Focus & Depth of Field
To begin making use of focal effects, you must understand a fundamental property of focus manipulation: depth of field. Put simply, depth of field refers to the range in front of your lens that will be in sharp focus when you shoot. Depth of field is important because it allows you to precisely control the elements in your image that are in or out of focus.
Many things impact the depth of field; the three primary variables are the focal length of your lens (wide angle or telephoto setting), the distance from the lens to your subject and the iris diameter (see Figure 1):
Depth of Field is compressed as you zoom in on your subject and expanded as you zoom out.
Depth of Field increases as the distance between your subject and the lens increases.
Depth of Field increases as iris diameter decreases.
You can learn to direct these variables to achieve the desired focal result. For example, you will no doubt shoot a lot of footage in which you want everything in the shot to be in sharp focus. As such, you want the depth of field to be as long as possible, extending from your lens all the way back to the horizon. Because depth of field increases as the distance between your subject and the lens increases, you can achieve your desired focal result if you position your camcorder at a generous distance from your subject. Then, when you focus your shot, or when your camcorder's autofocus takes over, all components foreground, your subject and the background should be in sharp focus.
You can also adjust depth of field by manipulating the diameter of your camera's iris, either by reducing or increasing the brightness of the light on your shot so that you can decrease or increase iris diameter to increase or decrease depth of field. Be careful not to reduce light too much. Your shot will end up nicely focused, but dark and grainy.
If you have trouble getting everything in your shot into focus, try zooming in first on your background as tightly as you can. Get the background in focus, and then zoom out. The rest of the shot should then be in sharp focus.
You can use depth of field to perform what is called a "rack focus"selectively focusing on certain portions of your shot while blurring other portions. Essentially, you will be shifting focus from one subject to another - usually from the foreground to the background or vice versa - to highlight those subjects in turn.
A rack focus requires a very short depth of field. To achieve that short focal depth, position your camcorder back from your subject a bit and zoom in close to one of the subjects in question - as close to the foreground subject as possible for the shot (see Figure 2). Because depth of field increases as the distance between the lens and the subject increases, you are decreasing depth of field by closing the gap between your camcorder and your subject.
Begin by zooming in and focusing on the object in the foreground. Because the depth of field is very short, your entire background will probably be out of focus when the foreground is sharply focused. Now, manually re-focus your shot so that the background begins to come into focus. You will see the depth of field shift to the background and the foreground object will drift out of focus. You can use this technique to toggle your focus between the background and foreground of your shot for a unique visual effect.
You will no doubt find yourself in situations where your subject is moving. A moving subject poses a problem because your subject can move in and out of focus as he moves toward or away from the camcorder. What can you do to ensure that your subject is always in focus?
Your camcorder's autofocus will usually do a pretty good job keeping your subject in focus. If the depth of field is short, however, you may have instances in which your shot frequently goes in and out of focus as your camcorder struggles to keep up with your subject. In these cases, it's best to take the controls manually.
If you find yourself shooting a moving subject in a shallow depth of field, you're going to have just as hard a time playing with the lens as your camcorder would in autofocus mode. Try to put a reasonable distance between you and your subject, and shoot in well-lit settings. Don't stand too far away, or else your subject won't be your subject anymore; he'll be background. By keeping the distance between you and your subject reasonable, you will be able to maintain an adequate depth of field. You may also have the luxury of pumping more light onto your shot. As the amount of light entering the lens increases and your iris closes down, depth of field increases.
Then, as your subject moves around, he should remain within your depth of field most of the time and, as such, in focus. As he begins to wander off toward the edges of your depth of field, you may see him begin to blur a bit. Bringing him back into focus, however, will require only the smallest manual adjustments of the camcorder's lens to compensate for depth of field. And because these adjustments are small and infrequent, you will be less likely to accidentally throw your subject way out of focus because you turned the lens too far too fast.
How can you control focus to create a unique transition between scenes? Well, you will find that by rapidly blurring your shot at the end of one scene and blurring the beginning of the next, you can create a nifty transition between the two.
To do this, manually blur the shot as much and as quickly as your camcorder will allow at the end of the first scene. Then pause the camcorder and set up your next shot. Before your start recording, though, manually blur the shot again. Now you can roll tape. The blur will look similar to the blur you just recorded at the end of your previous shot. To bring the shot back into focus again, simply press that "focus" button to reactivate autofocus. Your camcorder will quickly focus the shot again and you will have a neat blurred transition between your two scenes.
Because so many camcorders focus shots for you, it's easy to toss focus techniques aside as something you don't need to learn because a more high-tech solution is available to you. Mastering focal techniques, though, is just as important as learning camera moves, proper lighting and other camera techniques. As part of your video toolbox, focal techniques help you fine tune your program to make it look more polished and professional.