Using the Zoom Lens

Once you’ve set the focus, the next basic skill is learning how to use a zoom lens.

Camera lenses fall into two categories: prime lenses and zoom lenses. Prime lenses have a fixed focal length, measured in millimeters, that determines their angle of view. Prime lenses are known for producing a sharper image than zoom lenses, and DPs who work in feature films are used to having a selection of high-quality prime lenses for their 35mm film or digital cinema cameras.

If your camera can use interchangeable lenses, you will have the choice of using primes or zooms, or a combination of both for different shooting situations. However, most video cameras are equipped with built-in zoom lenses (Figure 7.5) that offer a range of focal lengths from telephoto (or close-up) to wide angles.

And that’s why learning to use the camera starts with learning to use a zoom lens. (Using prime lenses is discussed in Chapter 10.)

Figure 7.5

A professional zoom lens will be equipped something like this.

Focal Length Equivalency

Many people are familiar with the focal lengths of lenses used in 35mm. But whenever you use a camera with an image sensor that is smaller than 35mm film, the focal lengths are designed at a different scale. You can use a focal length multiplier to figure out the focal length equivalency of different lenses. For example, a 7mm DV lens has a focal length multiplier of 7 and is the equivalent of a 50mm lens on a 35mm still camera. Refer to the manufacturer’s documentation to get the focal length multiplier for your camera/lens.

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The great thing about a zoom lens is that it provides great flexibility when you frame a shot. Without changing your position, you can quickly zoom in to a subject to get a tighter view and a different framing. However, it’s essential that you pay attention to the elements of your image that change when you zoom in and out.

It’s easy to think of your zoom lens as a big magnifying glass and, to a degree, that is what it is. As you zoom in, your subject appears larger. This is why digital video camera manufacturers label their lenses with a magnification factor—2x, 3x, and so forth. However, a few other things happen to your image when you zoom.

Focal Length Defined

Focal length is the distance from the lens to the camera’s image sensor(s), usually measured in millimeters.

As you go to a longer focal length (zoom in), your field of view gets narrower. The human eye has a field of view of about 50 to 55°. This is considered a “normal” field of view (see Figure 7.6).

More important, though, is to pay attention to the way that a lens magnifies different parts of your image, and how it compresses depth overall as you zoom in and out.

At wider focal lengths (that is, when you are zoomed out), objects that are closer to the lens get magnified more than objects that are farther away. Telephoto lenses, on the other hand, magnify all objects in a scene equally, no matter how far away they are.

Here is an example. At some time, you’ve probably looked at a photograph or video of yourself and thought “that doesn’t really look like me.” One reason for the poor result might be that the photographer was using a wide-angle lens. Shooting a portrait with a wide-angle lens is problematic because some parts of your subject’s face are closer to the lens than others are. Consequently, those parts, particularly the nose, will be magnified more than the parts that are farther away.

Check out the pictures in Figure 7.7. The image on the left was shot with a slightly telephoto lens and really does look like the actual person. The image on the right is not a very good likeness (though it might be truer to this person’s character). The nose is too big and the ears have been rendered too small. In addition, the distance between the nose and ears—the depth of the picture—is too long. In other words, the sense of depth in the second image has been expanded, and the results look a bit weird.

Now consider the images in Figure 7.8. For these images, we zoomed the lens in, but we also changed the camera’s position to keep the framing the same. In other words, we adjusted the camera’s position (by moving it farther away) to maintain the same field of view as we zoomed the camera in. Therefore, the man appears to be the same size in each image, but notice what happens to the tree. It gets bigger! This is because, as we zoom in, we’re compressing the sense of depth in the image, just as we compressed the face of the man in Figure 7.7.

The lesson here is that there’s a price to pay for being lazy. Many people think “Great, I can stand here, zoom in, and get the shot I need, rather than having to take my camera all the way over there.” However, as you can see, the camera’s position and distance from the subject has a huge effect on the final image. A tight shot created by a zoom can feel voyeuristic, while a tight shot created by moving the camera up close can feel more intimate. In other words, your choice of camera position and corresponding focal length can greatly change the sense of space and atmosphere in your scene.

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Figure 7.7

These two pictures show what a difference focal length can make.

The image on the left was shot with a slightly telephoto focal length, while the image on the right was shot with a very wide-angle focal length.

Next time you watch a comedy, pay attention to the focal length of most shots. If it’s a particularly wacky comedy, you’ll probably notice that most close-ups and many scenes are shot with a really wide-angle lens. The fact is that wide-angle lenses make people funny-looking. You’ll be able to spot a wide-angle shot because actor’s faces will appear distorted as they are in the top two photos in Figure 7.8. You’ll also probably notice that objects behind the actors appear very far away, and you’ll have an extremely wide angle of view that encompasses a lot of the set or location.

To sum up: As focal length increases, the sense of depth in the image decreases, so it’s very important to carefully choose your focal length and camera position.

You’ll learn more about the importance of focal length when we discuss composition and framing later in this chapter.

Care of the Lens

Always keep your lens cap on when your camera is not in use. Keep a UV haze filter on your lens as a protective layer. Avoid touching the lens with your bare hands, since the oil from your fingers can etch a permanent mark on the glass. Never clean a lens with dry fabric or tissue. Instead, use a lens tissue dampened with lens cleaning fluid to wipe it off.