Closed loop automatic focusing unit

Claim 1

A closed loop automatic focusing system comprising: means for producing a beam of non-visible radiation directed towards and reflected from an object; afocal objective lens means for refracting the beam of non-visible radiation reflected from the object and visible light radiation reflected from the object, the lens means having the characteristic of refracting the reflected beams of non-visible radiation and the reflected visible light radiation in divergent or convergent form when the object is not in focus and refracting the reflected beam of non-visible radiation and reflected visible light radiation in collimated form when the object is in focus; means for sampling the beam of non-visible radiation and visible light radiation refracted from the lens means to produce a single sampled portion; means, acting upon the single sampled portion, for separating the reflected beam of non-visible radiation from the visible light radiation, the separation means having the characteristics of diverting the visible light radiation to a viewfinder and transmitting the beam of non-visible radiation; sensing means in the path of the transmitted beam of non-visible radiation for sensing a condition of divergence or convergence of the transmitted beam to provide an error signal; said sensing means comprising a double photo-sensitive cell, having adjacent photocell elements whose boundary is perpendicular to the path of movement of the transmittted beam of radiation as the object is brought into focus; and servo means responsive to the error signal for adjusting the lens means to bring the object into focus.