Lens construction for character projection units

Claim 1

IN A PROJECTION DISPLAY APPARATUS HAVING A RECTANGULAR TRANSLUCENT VIEWING SCREEN ADAPTED TO BE VIEWED FROM THE FRONT AND A PLURALITY OF CONVERGING PROJECTION SYSTEMS MOUNTED WITHIN A CONFINED VOLUME BEHIND THE SCREEN FOR SELECTIVELY PROJECTING DIFFERENT CHARACTERS ONTO THE SCREEN FROM THE REAR AND INCLUDING A PLURALITY OF LIGHT SOURCES CONSTITUTING A SEPARATE SOURCE FOR EACH SYSTEM THE IMPROVEMENT WHICH COMPRISES A LENS PLATE OF TRANSPARENT MATERIAL DISPOSED BETWEEN THE LIGHT SOURCES AND BEHIND THE SCREEN AND HAVING AN APPROXIMATELY SPHERICAL CURVATURE ON A RADIUS FROM THE CENTER OF THE SCREEN, AND A PLURALITY OF INDIVIDUAL CONDENSING LENSES FORMED INTEGRALLY WITH THE PLATE MATERIAL, EACH LENS HAVING AN OPTICAL AXIS ALIGNED WITH THE AXIS OF PROJECTION OF A RESPECTIVE ONE OF SAID CONVERGING PROJECTION SYSTEMS, AND EACH LENS BEING IN THE FORM OF A FIGURE OF REVOLUTION ABOUT ITS OPTICAL AXIS WITH THE PERIMETER OF THE LENS BEING CHOPPED OFF ON A PLURALITY OF SIDES SO THAT THE LENS HAS AN APPROXIMATELY POLYGONAL OUTLINE WHEREBY A GREATER IMAGE BRIGHTNESS IS ACHIEVED WITHIN THE LENS PLAE SIZE LIMITATIONS IMPOSED BY SAID CONFINED VOLUME.