How to: Exposure Controls

One of the least understood exposure controls deals with what is usually called "back light compensation". Basically this allows the camera to adjust its exposure to counteract strong light entering the scene from the background area. Indoors this is usually the result of a nearby light or window. I'm sure you've noticed before that when shooting someone who is seated beside a lamp every time you point the camera anywhere near the lamp the rest of the scene gets very dark. This generally causes the main subject to become silhouetted, wiping out facial features and other details.

The way it works is that when you engage the backlight compensation, the camera adjusts by opening the lens iris. This will result in the rest of the scene being overexposed, but the idea is to achieve the proper exposure for the main subject. You can help the situation by staying zoomed in as tightly as possible. Even though to your eyes the offending light source doesn't look all that bright, it doesn't take much to overwhelm a video camera. Video does not see light and dark with the same subtle gradations that film does. Therefore, video is much more sensitive to differences of bright and dark. Sometimes video cameras find it very difficult to correctly set the exposure for one part of a scene without adversely affecting the other parts of the scene.

This problem of dealing with extreme light and dark is also very pronounced when shooting stage productions. Parts of the stage are very dark, while others are very strongly lit. This will cause the bright parts of the scene to be washed out, which means very little contrast and color due to the overwhelming amount of light. Occasionally, the effect will be so pronounced that the whiteness seems to explode out into the rest of the scene, and sometimes seems to turn blue or green. This phenomenon is known as "blooming", and should be avoided at all costs. In extreme cases, blooming can actually damage components inside the camera, and even in less severe cases, can distort the audio track and cause the video signal to become unstable. At the very least, blooming wrecks the overall quality of the footage to the point that it is nearly unusable.

Most of today's camcorders also have another valuable exposure control tool. They have auto-exposure "modes" that are designed to more accurately handle certain shooting conditions. For example, there may be a stage setting, a sand/snow setting, and even a sports mode. These various modes are preprogrammed to override the normal exposure parameters. In the case of the stage and sand settings, the camera compensates by closing the lens down farther than would normally be called for by the meter. This results in a more correct exposure for the bright areas, which is the opposite of what happens with backlight compensation. Sports mode is designed not so much for exposure, but for stopping the action in faster sports by using a higher shutter speed. One of the by-products of this, however, is that the faster the shutter speed, the less light enters the camera. So actually a different shutter speed also affects the exposure equation.

Experiment to find out what works best for you. But whatever you do, learn how to use these valuable tools. They really can make your life a lot easier, and your videos a lot better.