Camcorder Binoculars: Getting Close with Telephoto

by Gene Bjerke
November 1998

Using a telephoto lens is like giving your camcorder a pair of binoculars. The longer the focal length the greater the magnification.

The cameraman was nose to nose with the rattler . Its forked tongue flicked in and out as its beady eyes fixed him with an unblinking stare. Instinctively, he pulled his head back from the viewfinder to assure himself that the snake, whose face filled the frame, was still 20 feet away. Such is the impact of a telephoto lens that even an experienced wildlife photographer needed to make sure that the viper hadn't somehow slithered up on him.
This experience from a shoot I worked on illustrates the most common use of the telephoto lens: to bring that which is distant up close. In this case, the viewer saw a ground level, bigger-than-full-screen closeup of a coiled rattlesnake. The shot made a real impact. Your camcorder comes with a built-in telephoto lens in the form of a variable zoom lens.

Lens Look
To take full advantage of your telephoto lens, you need to understand how it works. To get an idea of how it operates, take a piece of paper and cut a hole, say 1.5 × 2 inches. Hold it in front of your face and peer through it with one eye. As you move the paper toward or away from your face, the amount you can see through the hole will change. This mimics the effect of different focal length lenses. Like holding the piece of paper out at arm's length, the piece of the world you can see (called the field of view) becomes very narrow at long focal lengths. This makes following a moving subject more difficult. A relatively small movement on the part of your subject can take it right out of the frame. Something in constant motion (such as a surfer or racecar) is easier to follow than something that moves unpredictably (such as a wild animal).

Magnification
People who shoot wildlife or surfing competitions use really long lenses to bring that distant person or animal up close for a good look. Telephoto lenses let you see the details of something far off. However, this comes with some inherent problems.
Telephoto lenses magnify camera movement as well. Like looking through very powerful binoculars, you need to hold the instrument absolutely steady. This means that you should use a tripod for telephoto shots unless your camera has very good image stabilization (See Loren Alldrin's story Image Stabilization: High-tech Help for Shaky Shots on page --X of this issue) and even then, a tripod is a good idea. Moves, such as panning and tilting, need to be done more slowly than usualunless you want to give the impression of the world flying by at high speed.

Perspective Effects
Telephoto lenses flatten perspective. They make different elements in the picture look closer together than they really are. You've seen this in movies where the hero seems to be walking down an incredibly crowded street with people squeezed right up next to him. You get this effect by standing well back and shooting with a long telephoto lens. All the people in the scene seem to be pushed together into the same little space.
This is a natural function of looking closely at something far away. For example, look at the two illustrations of beach scenes. One was taken with a normal lens (figure 1a), one with a telephoto (figure 1b). The beach looks much more crowded in the telephoto shot. But if you look at the area of the wider shot inside the white rectangle, you will see the same effect as the telephoto. In fact, if you were to take just that part of the shot and blow it up, it would look the same as the telephoto shot. This, in effect, is how a digital zoom works.
Besides making things look more crowded, this perspective effect can be useful in other ways. For instance, say you want to shoot your talent next to a large animal, such as a cow or horse, but every time she gets near the animal it gets agitated or moves away. Just place your talent about 20 feet in front of the animal (figure 2a) and zoom in for a telephoto shot (figure 2b). The lens will compress the distance between the person and the animal, making them appear closer together.

Depth of Field
Telephoto lenses have less depth of field than shorter lenses. That means the area of acceptable sharpness at a given point of focus is shallower in long focus lenses than in shorter ones. Controlling depth of field is just one more tool for the creative videographer.
A lens is sharpest at the point on which it is focused. The image of objects closer or farther away from that point gradually becomes softer. At a certain point this softness becomes noticeable and we say that an object is "out of focus." The range of distances from the camera (say from 10 to 30-feet) in which objects are acceptably sharp is called depth of field (figure 3). Depth of field is a gradual and subjective thing. You won't have something at 9-feet be a total blur and something at 10-feet be razor-sharp. But once it's out of focus, you'll definitely know it.
Three elements contribute to depth of field: focal length, distance from the camera, and aperture.
-- The farther from the camera you focus, the greater the depth of field.
-- The longer the focal length of the lens, the shallower the depth of field.
-- The smaller the aperture, the greater the depth of field.
In some situations, the first two factors will cancel each other out. If you maintain the same framing by using different focal lengths to shoot from different distances, the depth of field will depend entirely on the aperture. This is usually only a problem if you find you do not have enough depth of field for a given subject. In that case, the solution is to provide more light on the subject so that you can use a smaller aperture.
For most shooting, by adjusting the point on which the lens is focused you can place this band of sharpness where it will be the most effective. You can emphasize your subject and throw everything else out of focus. Telephoto lenses, with their narrower depth of field, generally give you more control over this.

Creative Controls
The magnification of a telephoto can be used for dramatic effect. For example, you may want to shoot a twilight shot that includes the full moon in the background. The moon will appear larger and closer if you shoot with a long lens (figure 4).
You can also zoom in on objects that aren't so far away. While a telephoto lens usually will not focus close enough to be a true macro lens (used for very detailed close-ups), it will often enable you to take interesting close-ups or details. At close range, the shallow depth of field of a telephoto will also help the item stand out from its background.
On even normal-sized subjects, you can minimize distracting backgrounds using depth of field. If possible, move your subject away from the background and adjust your focus to soften the background but keep the subject sharp.
Manipulating perspective is a useful creative tool. If you want to associate two things that are separated, move back and shoot them with your telephoto. This will make them appear closer together. On the other hand, if you want to emphasize their separation, a wide-angle lens will accomplish that. It's just as important to know when not to use a telephoto.
To be creative, you need to know your equipment, what it can do, and what it can't. The telephoto lens is just one of your creative tools. By learning its characteristics and visual effects, you can use this tool to increase the impact of your videos.

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What is a Telephoto Lens?
Lenses are classified according to focal length. That is the distance from a point inside the lens called the focal point to the point where the image is captured (see figure). In a camcorder, this point of capture is called the CCD, or charge coupled device. The CCD is a light-sensitive silicon wafer that converts images to electrical impulses, which are then captured on the actual film. Each focal length puts an image of a different piece of the world in your camera. Short focal lengths show a wider area and long focal lengths have a narrower field.
For each camera there is a "normal" lens. This is the focal length that places an image on the screen that is close to what you normally see with your eye. A normal lens is defined as one whose focal length equals the diagonal measurement of the CCD. For most camcorders that comes to 912mm. Lenses much shorter than that are wide-angle lenses, lenses longer than about twice normal are long-focus or telephoto lenses.
Most camcorders have a single lens of variable focal length, called a zoom lens. This enables the videographer to carry the equivalent of a large number of lenses in one unit. Your camcorder's zoom lens, zoomed in to about 20mm, acts as a telephoto lens and has all the characteristics of one.

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