Almost 30 years ago, when film was king and video was in its infancy, photographer George Wallace had an idea. An avid devotee of American nature photographer Ansel Adams and his “zone” system, Wallace developed a simple glass converter to turn a film camera into an incident light meter.

He would never know (Wallace died in 2001), but his work led to the development of ExpoDisc, a technology that aids both digital still and video photographers in achieving a more accurate white balance reading while on location.

The ExpoDisc Digital White Balance Filter helps videographers eliminate blue, green, red and yellow colorcasts often encountered when shooting under varying lighting conditions. Basically, the system substitutes a glass filter for an 18 percent gray card when measuring incident light.

Each ExpoDisc is hand-calibrated to fall within strict tolerances of light transmission and color neutrality, and is guaranteed to be within +/- 2 percent of neutral, according to the company.

To adjust white balance, you mount an ExpoDisc in front of a video camera’s lens and use the white balance function. That’s it. No cards are needed and there’s no need to worry about the accuracy of the camera’s auto white balance measurement. The camera neutralizes the color cast it sees through the ExpoDisc.

Expoimaging, the Morgan Hill, CA, ExpoDisc manufacturer, says its product receives, scrambles and passively transmits mixed light from a wide angle in front of the disc through to the image sensor for a more accurate and efficient white-balance correction than from an 18 percent card.

ExpoDiscs are available in six standard sizes from 58mm to 82mm. Additional sizes are available in 4×4 and 4×5.65 configurations for video filter box systems from Arri, Century, Chrosziel, Lee, and Schneider. Prices range from about $100-125, depending on size.

For more information, visit www.expodisc.com.