Auto-focus movie camera

Abstract

The lens mount of a movie camera is automatically positioned to maintain an image of a subject in focus on a focal plane of a recording station by generating periodic range pulses having a characteristic directly related to subject range, and converting each pulse to a number which represents the focus position of the lens mount. Such number is stored in a first register whose contents vary in response to changes in subject distance at a rate dependent on the pulse repetition rate of the range pulses. The actual position of the lens mount is determined in the form of a second number which is stored in a second register whose contents vary in response to changes in the position of the lens mount at a rate determined by the rate of change of position. Rotation of a reversible motor is initiated when the contents of the registers are unequal, rotation being terminated when the contents are equal. The direction of rotation is in accordance with which of the two registers has the larger contents. Alternatively, rotation is initiated only after it is determined that the contents of one register exceeds the other over a majority of a predetermined number of range pulses, the direction of rotation being determined by which of the two registers has the larger contents a majority of the time over such predetermined number of range pulses.