Block type albada viewfinder with indicator viewing mirror and lens carried by frontelement

Claim 1

A BLOCK TYPE ALBADA DISTANCE MEASURNG AND RANGING VIEWFINDER, FOR PHOTOGRAPHIC CAMERAS, COMPRISING, IN COMBINATION, A FRONT OBJECT FACING LENS HAVING A CONCAVE INNER SURFACE; INTERMEDIATE BLOCK MEANS, OF TRANSPARENT MATERIAL, HAVING A CONVEX OBJECT FACING END SURFACE FORMING AN INTERFACE WITH SAID CONCAVE SURFACE; A PARTIALLY LIGHT-PERMEABLE MIRROR DISPOSED IN SAID INTERFACE; A REAR OPTICAL ELEMENT, OF TRANSPARENT MATERIAL, HAVING AN OBJECT FACING SURFACE FORMING AN INTERFACE WITH THE EYE FACING END SURFACE OF SAID BLOCK MEANS; AN IMAGE LIMITING FRAME DISPOSED IN SAID LAST-NAMED INTERFACE IN SUBSTANTIALLY THE FOCAL PLANE OF SAID MIRROR FOR IMAGING BY THE LATTER AT SUBSTANTIALLY INFINITY A PARTIALLY LIGHT-PERMEABLE OBLIQUE MIRROR IN SAID INTERMEDIATE BLOCK MEANS INTERSECTING THE OPTICAL AXIS OF SAID VIEWFINDER INWARDLY OF SAID MIRRORED INTERFACE AND FACING SAID REAR OPTICAL ELEMENT; AND OPTICAL SYSTEM DISPOSED LATERALLY OF SAID INTERMEDIATE BLOCK MEANS AND EFFECTIVE TO DIRECT LIGHT RAYS FROM THE OBJECT LATERALLY INTO SAID INTERMEDIATE BLOCK MEANS AND TO SAID OBLIQUE MIRROR, SAID OBLIQUE MIRROR DIRECTING THE LATTER LIGHT RAYS TO THE EYE OF AN OBSERVER LOOKING THROUGH THE VIEWFINDER; A SLOT FORMED IN A LATERAL SURFACE OF SAID FRONT LENS, LOCATED IN ITS ENTIRELY IN THE VICINITY OF SAID LATERAL SURFACE OF SAID FRONT LENS, SPACED FORWARDLY FROM SAID INTERMEDIATE BLOCK MEANS, AND SAID SLOT BEING A BLIND BORE WITH PARALLEL SIDE WALLS FORMED IN THE FRONT PORTION OF THE LATERAL SURFACE OF THE FRONT LENS AND EXTENDING INWARDLY AND OBLIQUELY TO TERMINATE FORWARDLY ON THE CANCAVE INNER SURFACE AND EXTENDING GENERALLY OBLIQUE TO THE OPTICAL AXIS OF THE VIEWFINDER; A REFLECTING MIRROR POSITIONED IN SAID SLOT IN THE PATH OF LIGHT RAYS FROM AND INDICATOR OR THE LIKE LOCATED LATERALLY EXTRANEOUS OF THE VIEWFINDER; AND A PLANO-CONVEX COLLIMATOR LENS MOUNTED ON SAID LATERAL SURFACE OF SAID FRONT LENS IN ADVANCE OF SAID REFLECTING MIRROR WITH ITS PLANO SURFACE CEMENTED TO THE LATERAL SURFACE OF SAID FRONT LENS IN ALIGNMENT WITH THE REFLECTING MIRROR IN SAID SLOT, SAID PATH OF LIGHT RAYS EXTENDING THROUGH SAID COLLIMATOR LENS TO SAID REFLECTING MIRROR AND SAID COLLIMATOR LENS BEING DESIGNED AND CONSTRUCTED TO PROVIDE AN IMAGE OF THE INDICATOR, OR THE LIKE, AT SUBSTANTIALLY INFINITY IN THE FIELD OF VIEW OF AN OBSERVER LOOKING THROUGH THE VIEWFINDER, SAID COLLIMATOR LENS BEING SITUATED IN ITS ENTIRELY FORWARDLY OF AND IN NON-OVERLAPPING RELATIONSHIP WITH RESPECT TO SAID INTERMEDIATE BLOCK MEANS, AND SAID REFLECTING MIRROR BEING ORIENTED AND ARRANGED TO REFLECT SAID LIGHT RAYS TO THE EYE OF AN OBSERVER LOOKING THROUGH SAID REAR OPTICAL ELEMENT, TO PROVIDE AN IMAGE OF THE INDICATOR OR THE LIKE AT SUBSTANTIALLY INFINITY IN THE FIELD OF VIEW OR SUCH OBSERVER; WHEREBY DUE TO THE POSITIONING OF SAID REFLECTING MIRROR IN SAID SLOT AND SAID PARTIALLY LIGHT-PERMEABLE OBLIQUE MIRROR IN SAID INTERMEDIATE BLOCK MEANS, INTERFERENCE BETWEEN THE LIGHT RAYS DIRECTED BY THE SAID OPTICAL SYSTEM LATERALLY INTO SAID INTERMEDIATE BLOCK MEANS AND THOSE PROVIDING SAID IMAGE OF THE INDICATOR OR THE LIKE IS PREVENTED.