Ensuring Accurate White Balance
Why is it that sometimes you end up with blue faces, even when you know you white-balanced your camera before making a shot? The possible causes are simple and rather limited. There might have been something in the shot that was brighter than your white reference, perhaps a window or other light source. Or your assistant might have held the white card so that light from a fluorescent or tungsten lamp on one side of the room illuminated it when the camera was positioned so that a nearby window had a greater influence on the lighting. Perhaps the white-balance was done with a camera-mounted light illuminating a white card held five feet from the lens while the subject was 15 feet away -- too far for the camera light to have the same effect.
Following two basic rules will ensure accurate and predictable white-balances. First, always be sure that the white you have chosen to balance on is the brightest object in the shot. While most professional cameras do not require that you fill the entire frame with white, you should always zoom in enough to exclude windows or anything else the camera could mistakenly choose as a reference. And remember that failure to keep the white card in focus can allow color from adjacent parts of the shot to pollute the white.
Second, always position the white card so it is vertical, aimed directly at your camera, and positioned at the most critical part of the shot. Since we most frequently are photographing people, and since skin tones are most likely to reveal even minute color shifts, the best place to hold the white card is directly in front of the principal subject's face. Tilting the card upward will allow ceiling mounted lamps to have a greater influence on your balance than they do on the overall scene. And in cases where there is a mixture of lighting sources, aiming the card at anything but your lens will prevent the white-balance from accurately assessing the mix. In the next Sharpshooters' Tips we'll look at the color temperature values displayed in the viewfinder and decode their cryptic message.