Combined viewfinder and rangefinder with composite birefringement prism assembly for photographic cameras

Claim 1

A COMBINED VIEWFINDER AND RANGEFINDER FOR PHOTOGRAPHIC CAMERAS, COMPRISING A FINDER OBJECTIVE, AN IMAGE INVERTING SYSTEM, AND AN EYEPIECE LENS FORMING AN OPTICAL SYSTEM WITH AN OPTICAL AXIS ALONG WHICH SAID OBJECTIVE IS MOVABLE, A BEAM COMBINER ARRANGED ON THE OPTICAL AXIS BETWEEN THE OBJECTIVE AND THE IMAGE INVERTING SYSTEM, SAID BEAM COMBINER BEING COMPOSED OF THREE TRIANGULAR SHAPED PRISM ELEMENTS ARRANGED IN CONTACT IN ALTERNATE OPPOSED RELATION, OF WHICH AT LEAST TWO CONSIST OF OPTICALLY DOUBLE REFRACTIVE MATERIAL WITH THEIR OPTICAL AXES NORMAL TO THE AXIS OF THE OPTICAL SYSTEM AND ANGULARLY DISPLACED ONE FROM THE OTHER 90*, SAID TRIANGULAR PRISMS BEING ARRANGED SO THAT THE OUTER WALLS OF THE OUTERMOST PRISMS EXTEND IN PARALLEL RELATION AND PERPENDICULAR TO THE AXIS OF THE OPTICAL SYSTEM, SAID BEAM COMBINER BEING LOCATED ON THE OPTICAL AXIS AT A POSITION ENCOMPASSING THE FOCAL PLANE OF THE FINDER OBJECTIVE, SAID BEAM COMBINER BEING OPERATIVE TO DEVIATE IMAGE RAYS FORMING TWO PARTIAL RAY PATHS FROM OPPOSITE LATERAL PORTIONS OF THE FINDER OBJECTIVE INTO COINCIDENCE WHEN THE FINDER OBJECTIVE IS PROPERLY FOCUSED, THE COINCIDENCE FOCAL PLANE OF THE BEAM COMBINER BEING PERPENDICULAR TO THE OPTICAL AXIS, THE PARTIAL RAY PATHS BEING SYMMERTICAL TO THE OPTICAL AXIS AND HAVING AN INCLUDED ANGLE OF AT LEAST 5*, AT LEAST ONE POLARIZER LOCATED ON THE OPTICAL AXIS ADJACENT THE EYEPIECE FOCAL PLANE, COVERING THE ENTIRE EYEPIECE IMAGE AND ORIENTED TO BLOCK THE POLARIZED LIGHT COMPONENT OF ONE PARTIAL RAY PATH AND TRANSMIT THE POLARIZED LIGHT COMPONENT OF THE OTHER PARTIAL RAY PATH AND A BIREFRINGENT ELEMENT OF REDUCED SIZE COMBINED WITH AND POLARIZER AND DISPOSED ADJACENT THE SIDE OF THE POLARIZER FACING THE INCOMING LIGHT RAYS AND PRODUCING A PHASE RETARDATION OF $/4 IN THE PATH OF THE LIGHT RAYS TO DEFINE A REDUCED COINCIDENCE IMAGE RANGEFINDING AREA.