Four-component objective having two movable components

Claim 1

AN OPTICAL OBJECTIVE COMPRISING A BICONVEX DOUBLET L7, L2 CONSTITUTING A FIXED POSITIVE FIRST COMPONENT I, A LENS L3 CONSTITUTING A NEGATIVE SECOND COMPONENT II, A LENS L4 CONSTITUTING A NEGATIVE THIRD COMPONENT III, AND A FIXED POSITIVE FOURTH COMPONENT IV CONSISTING OF A PLURALITY OF AIR-SPACED LENS MEMBERS L5, L6, L7, L8; SAID SECOND AND THIRD COMPONENTS BEING MOVABLE, RELATIVELY TO EACH OTHER AND TO SAID FIRST AND FOURTH COMPONENTS, INTO A FIRST POSITION IN WHICH THE OBJECTIVE HAS A RELATIVELY SMALL FOCAL LENGTH, A SECOND POSITION IN WHICH THE OBJECTIVE HAS AN INTERMEDIATE FOCAL LENGTH, AND A THRID POSITION IN WHICH THE OBJECTIVE HAS A RELATIVELY LARGE FOCAL LENGTH; SAID LENSES L1 TO L8 HAVING RADII OF CURVATURE R1 TO R15 AND THICKNESSES AND SEPARATIONS D1 TO D14 WHOSE NUMERICAL VALUES, BASED UPON A VALUE OF 100 UNITS FOR AN INTERMEDIATE OVERALL FOCAL LENGTH, TOGETHER WITH THEIR REFRACTIVE INIDICES ND AND ABBE NUMBERS V ARE SUBSTANTIALLY AS GIVEN IN THE FOLLOWING TABLE, WITH THE SPACINGS D3, D5 AND D7 GIVEN FOR SAID SECOND POSITION: