Active-type auto-focusing mechanism

Claim 1

An active-type auto-focusing mechanism, comprising: a light projector having a light projection lens for projecting light from a light source toward an object; a photo detector having a plurality of position sensing devices, disposed at predetermined distances from the light projector and positioned to receive the projected light beam reflected from the object, and to produce photo currents corresponding to the amount and intensity of the light received thereby; and a processor for receiving the photo currents produced by said position sensing devices, and calculating the distance between the object and film surface based on said photo currents; said position sensing devices being comprised of first and second position sensing devices each having position-sensitive photo-detection elements disposed at predetermined equal distances in mutually opposite directions from, and centered with respect to, said light projector; said processor comprising means for summing the amplitudes of the photo currents produced by each position sensing device, thereby preventing erroneous distance measurement caused by incorrect projections, partial reflection of the light beam or movement of the object.