Four-component varifocal attachment with movable negative lens members

Claim 1

A VARIFOCAL ATTACHMENT FOR AN OPTICAL OBJECTIVE, CONSISTING OF FOUR COMPONENTS SEPARATED FROM ONE ANOTHER BY VARIABLE AIR SPACES AND TOGETHER CONSISTING AN AFOCAL SYSTEM, SAID COMPONENTS INCLUDING A FIXED FRONT COMPONENT OF POSITIVE REFRCATIVELY CONSTITUTED BY TWO AIR-SPACED POSITIVE MEMBERS OF STRONG FORWARD CONVEXITY OF WHICH THE FIRST ONE IS A SINGLET AND THE SECOND ONE IS A DOUBLET, A FIRST MOVABLE INTERMEDIATE COMPONENT CONSTITUTED BY A DOUBLET OF NEGATIVE REFRACTIVITY, A SECOND MOVABLE INTERMEDIATE COMPONENT CONSTITUTED BY A DOBULET OF NEGATIVE REFRACTIVITY, AND A FIXED REAR COMPONENT OF POSITIVE REFRACTIVITY, SAID REAR COMPONENT HAVING A FOCAL LENGTH EQUAL TO AT MOST 75% OF THE FOCAL LENGTH OF SAID FRONT COMPONENT, THE FOCAL LENGTH OF SAID FIRST INERMEDIATE COMPONENT EXCEEDING THAT OF SAID SECOND INTERMEDITE COMPONENT IN ABSOLUTE VALUE AND DIFFEREING FROM IT BY AT MOST 25%, SAID REAR COMPONENT BEING A BICONVEX DOUBLET HAVING A FRONT SURFACE WHOSE RADIUS OF CURVATURE AT LEAST EQUALS IN ABSOLUTE MAGNITUDE THE RADIUS OF CURVATURE OF ITS REAR SURFACE, SAID BICONVEX DOUBLET FURTHER HAVING A COLLECTIVE INTERNAL SURFACE STRONGLY CURVED TOWARD THE IMAGE SIDE OF THE SYSTEM