Wide field optical viewer with concave mirror eyepiece

Claim 1

AN IMAGE-FORMING OPTICAL INSTRUMENT COMPRISING MEANS TO DEFINE A POSITION FOR AN OBJECT, IMAGE-FORMING MEANS HAVING POSITIVE POWER AND AN AXIS TO FORM AT A SURFACE IN SPACE INTERSECTED BY THAT AXIS A REAR AERIAL IMAGE OF AN OBJECT ON SAID POSITION-DEFINING MEANS, A PARTIALLY TRANSPARENT AND PARTIALLY REFLECTING MIRROR DISPOSED OBLIQUELY ACROSS SAID AXIS, THE INTERSECTION OF SAID AXIS WITH SAID MIRROR BEING ADJACENT TO THE INTERSECTION OF SAID AXIS WITH SAID SURFACE, AND A CONCAVE MIRROR HAVING ITS CONCAVE SIDE FACING SAID PARTIALLY TRANSPARENT MIRROR AND DISPOSED IN ONE OF TWO POSITIONS, THE FIRST POSITION FOR SAID CONCAVE MIRROR BEING THAT IN WHICH SAID CONCAVE MIRROR IS INTERSECTED BY SAID AXIS AS TRANSMITTED THROUGH SAID PARTIALLY TRANSPARENT MIRROR AND IS DISTANT FROM SAID SURFACE BY SUBSTANTIALLY ITS OWN FOCAL LENGTH, THE SECOND POSITION FOR SAID CONCAVE MIRROR BEING THAT IN WHICH SAID CONCAVE MIRROR IS INTERSECTED BY SAID AXIS AS REFLECTED IN SAID PARTIALLY TRSNSPARENT MIRROR AND IS DISTANT BY SUBSTANTIALLY ITS OWN FOCAL LENGTH FROM THE IMAGE OF SAID SURFACE IN SAID PARTIALLY TRANSPARENT MIRROR, THE NEGATIVE OF THE SUM OBTAINED BY ADDING THE PETZVAL CURVATURE CONTRIBUTIONS OF SAID IMAGE-FORMING MEANS TO THE RECIPROCAL OF THE RADIUS OF CURVATURE OF SAID OBJECT LYING BETWEEN ONE AND FOUR TIMES THE RECIPROCAL OF THE RADIUS OF CURVATURE OF SAID CONCAVE MIRROR.