Projected image positioning method and apparatus for photographic enlarger

Claim 1

Positioning apparatus for a photographic enlarger including a film holder, means for adjustably supporting said film holder in a selected position with respect to a sensitized material surface, said apparatus usable with a film containing at least one frame and having two register marks located at selected positions adjacent opposite sides of said frame and outside the image area of said frame, said enlarger having means for projecting said frame and said register marks toward said surface, comprising: at least two mirrors, each one positioned in the path of the projected image of one said mark, for diverting the projected image of said mark away from said surface; at least two sensors, one associated with each mirror, each comprising a receiver element having at least two electrically independent sections arranged symmetrically, and arranged to receive the respective diverted image of a register mark; means for mounting said sensors at the optical equivalent of the focal plane of the projected image of said register mark on said sensitized material surface when said film is in a position to project the image of said frame onto a desired frame location on said surface; means associated with said sensors for developing signals representative of the position of said projected register marks on said sensors and therefore of the position and orientation, relative to said sensitized material surface, of said enlarged projected image of said register marks; and means for adjusting the position and orientation of said holder comprising a feedback circuit connected to the sensors and adapted to activate at least one pulse motor for causing movement of the film holder rotationally about its center and rectilinearly in two perpendicular directions in the plane of the holder in response to said signals from said sensors to move said projected image to said desired frame location.