Automatic focusing system

Claim 1

In a photographic apparatus having a focusing lens movable along an axis for passing light from a far or near object toward stationary means adapted to align light sensitive media inside the apparatus, means for automatically moving the lens toward said stationary means when said object is far, and away from said stationary means when said object is near, comprising: emission means secured to said apparatus for transmitting a train of light signals toward said object at a constant angle relative to said axis; movable first and second photoreceptors disposed in spaced relationship in said apparatus; each of said photoreceptors adapted to simultaneously receive at least a portion of said light signals upon reflection thereof from said object, said first and second photoreceptors simultaneously producing, respectively, first and second electrical signals corresponding to the portions of said light signals received; signal translation means for receiving said electrical signals from said respective photoreceptors and producing a difference signal corresponding to the difference between said electrical signals; said difference signal having a first polarity when said first electrical signal is larger than said second electrical signal, and said difference signal having an opposite polarity when said second electrical signal is larger than said first electrical signal; mechanical means, responsive to said difference signal for causing movement of said lens relative to said stationary means in one direction when said difference signal is of said first polarity, and in the opposite direction relative to said stationary means when said difference signal is of said opposite polarity; said mechanical means being further adapted to cause simultaneous movement of said photoreceptors until the portions of said light signals at said photoreceptors are equalized to produce an absolute minimal difference signal indicative of said object being properly focused on by said lens; and gain means, having a first position for maintaining the amplification of said difference signal, and a second position for raising the amplification of said difference signal; said gain means being set to said first position when said lens is moved past a predetermined point on said axis away from said stationary means, said gain means being set to said second position when said lens is moved past said predetermined point toward said stationary means, whereby the amplitude of said difference signal is automatically increased when focusing on far objects.