Zoom lens system having front mounted axially movable aperture stop to control numerical aperture during magnification change

Claim 1

IN A MICROSCOPE, A ZOOM TYPE OF PANCRATIC OPTICAL SYSTEM COMPRISING, AN OBJECTIVE FORMED FROM A POSITIVE LENS GROUP AND A NEGATIVE LENS GROUP IN OPTICAL ALIGNMENT THEREWITH, SAID GROUP BEING MOVABLE AXIALLY SIMULTANEOUSLY AND CONTINUOUSLY AT DIFFERENT RATES WITH RESPECT TO A STATIONARY POINT ON THEIR OPTICAL AXIS SUCH THAT A SUBSTANTIALLY STATIONARY IMAGE IS FORMED OF A SPECIMEN BY THE SYSTEM THROUGH A CONTINUOUS PROGRESSION OF MAGNIFICATION INCLUDLING A MAGNIFICATION RANGE OF SUBSTANTIALLY 4, AND AN EYEPIECE ALIGNED WITH SAID OBJECIVE AND FOCUSED ON SAID STATIONARY IMAGE FOR VIEWING THE SAME, SAID POSITIVE LENS GROUP COMPRISING A FRONT BLOCK OF TRANSPARENT OPTICAL MATERIAL SPACED REARWARDLY FROM SAID SPECIMEN AND DESIGNATED I, AN APERTURE PLATE MOUNTED ON THE FRONT FACE OF SAID BLOCK, THE APERTURE THEREIN BEING ALIGNED OPTICALLY WITH SAID GROUP FOR VARYING THE NUMERICAL APERTURE OF THE OBJECT SIDE OF SAID SYSTEM SUBSTANTIALLY IN PROPORTION TO THE CHANGE OF MAGNIFICATION OF THE SYSTEM WHILE MAINTAINING THE NUMERICAL APERTURE ON THE IMAGE SIDE SUBSTANTIALLY CONSTANT, A FIRST AN A SECOND POSITIVE SINGLET LENS COMPRISED IN SAID POSITIVE GROUP AND SPACED REARWARDLY FROM SAID BLOCK AND FROM EACH OTHER AND DESIGNATED II AND IV RESPECTIVELY, THE LENS SURFACES THEREOF HAVING THE STRONGER CURVATURE FACING TOWARD EACH OTHER, A POSITIVE DOUBLET LENS DESIGNATED III COMPRISED IN SAID POSITIVE GROUP AND INTERPOSED BETWEEN SAID SINGLET LENSES AND SPACED AXIALLY FROM EACH, SAID DOUBLET LENS COMPRISING A FRONT NEGATIVE LENS ELEMENT AND A REAR DOUBLE CONVEX LENS ELEMENT IN CONTACT THEREWITH, SAID NEGATIVE LENS GROUP BEING OF DOUBLE CONCAVE FROM AND BEING DESIGNATED V,