Albada type viewfinder with image frame in composite rear lens assembly

Claim 1

AN ALBADA TYPE VIEWFINDER COMPRISING, IN COMBINATION, A FRONT, OBJECT-FACING LENS HAVING A CONCAVE INNER SURFACE CARRYING A PARTIALLY LIGHT-PERMEABLE MIRROR; A REAR LENS ASSEMBLY AXIALLY SPACED BY AN AIR GAP FROM SAID FRONT LENS AND MOUNTING AN IMAGE LIMITING FRAME IN SUBSTANTIALLY THE FOCAL PLANE OF SAID MIRROR FOR IMAGING BY THE LATTER AT SUBSTANTIALLY INFINITY, SAID ASSEMBLY INCLUDING A FIRST PLANO-PARALLEL OPTICAL ELEMENT TOWARD SAID FRONT LENS, A SECOND OPTICAL ELEMENT HAVING AN ANNULAR CONVEX SURFACE AND A CENTRAL PLANE SURFACE IN CONTACT WITH THE CENTRAL PORTION OF THE FACING PLANE SURFACE OF SAID FIRST OPTICAL ELEMENT AND A DISPERSION LENS OF TRANSPARENT, ADHERENT AND INITIALLY PLASTIC MATERIAL, HAVING AN INDEX OF REFRACTION EQUAL TO THAT OF SAID SECOND OPTICAL ELEMENT, DISPOSED BETWEEN AND FORMING INTERFACES WITH THE FACING SURFACES OF SAID OPTICAL ELEMENTS, AND HAVING AN ANNULAR CURVED AND CONCAVE SURFACE FACING AND IN CONTACT WITH SAID SECOND OPTICAL ELEMENT; SAID FRAME BEING DISPOSED ON SAID ANNULAR CONVEX SURFACE OF SAID SECOND OPTICAL ELEMENT; AND A CASING EMBRACING AND AXIALLY SPACING SAID FRONT LENS AND SAID REAR LENS ASSEMBLY.