Huntingdon Valley, PA--Viewers of "Casino," a film by Universal Pictures, may recall a scene where the camera follows a mob bagman. As this character wends his way through the underbelly of a glitzy Las Vegas gambling palace, the camera whips from the face of one patron to another, revealing arcane aspects of their world.
A camera stabilizing system, called Steadicam®, makes this piece of cinematography possible. Its operation depends, in part, on a tilt sensor and the artificial horizon the sensor generates. Displayed against a "Y" axis superimposed on the system's video monitor, the left or right side of the horizon moves up or down as the camera tilts.
"Earlier camera stabilizing systems relied on a standard bubble level," says Jim Bartell, director of electrical engineering at Cinema Products Corp., the manufacturer of Steadicam. The bubble level, he claims, gives some indication of camera orientation, but presents several problems.
Because the bubble level mounts on the video monitor bezel, the cinematographer must look away from the screen to view the level. This interrupts the operator's concentration and his or her ability to achieve an optimal shot. Bezel mounting also places the level away from the system's center of gravity, where lateral acceleration can adversely affect its readings.
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Designed and built by the Fredericks Company, the Micro-Arc proportional linear tilt sensor overcomes these limitations. Its tubular, toroidal construction minimizes the affects of lateral acceleration, as does its center-post mounting location. A Fredericks-licensed electronics board, which generates the required ac excitation remotely, drives the tilt sensor.
Each sensor consists of two precision-molded glass halves, hermetically sealed together. A channel in this envelope contains a partially conductive electrolyte that contacts precision-metalized electrodes. When the sensor is level, an equal impedance exists to the common electrode, and the digital voltmeter indicates a minimum, or null, output.
Tilting the sensor causes an unbalanced impedance to the common electrode. As a result, output voltage increases in proportion to the tilt angle. Output also includes a phase indicative of tilt direction. An A/D converter fed into a custom video-signal generator transforms the sensor readings to the visual horizon used by the Steadicam operator to gain the intended effect.
Bartell says the tilt sensor has another advantage over bubble sensors. For those shots where Steadicam operates upside down to bring the camera close to the ground, the sensor's toroidal shape eliminates repositioning and calibration.
Additional details, tilt sensor…Contact The Fredericks Company, 2400 Philmont Ave., Box 67, Huntingdon Valley, PA 19006-0067, (215) 947-2500.
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