Automatic focusing system

Abstract

This invention relates to photographic apparatus having means for automatically moving a lens along an axis for properly focusing on an object. The apparatus includes a light emitter for transmitting a train of light signals toward the object at a constant angle relative to the axis, and a pair of movable photoreceptors disposed in spaced relationship with the emitter in the apparatus. The photoreceptors are adapted to receive the light signals upon reflection thereof from the object, and are further adapted to produce electrical signals corresponding to the amount of light received. An operational amplifier is adapted to receive the electrical signals produced by the photoreceptors, and produce a difference signal corresponding to the difference in strength of the electrical signals. The apparatus further includes an electric motor, responsive to the difference signal, adapted to cause the movement of the lens along the axis, and further adapted to cause the movement of the photoreceptors until the amount of light received at each of the photoreceptors is equalized to produce an absolute minimal difference signal indicative of the object being properly focused by the lens. A gain change device is provided to increase the amplitude of the difference signal when relatively far objects are focused on.