Front attachment for optical objectives

Claim 1

A FRONT ATTACHMENT FOR AN OPTICAL OBJECTIVE, COMPRISING A DISPERSIVE COMPONENT, A COLLECTIVE COMPONENT FORMING A SUBSTANTIALLY AFOCAL SYSTEM WITH SAID DISPERSIVE COMPONENT, A REVERSIBLE SUPPORT FOR SAID COMPONENTS HAVING COUPLING MEANS FOR SELECTIVELY ATTACHING IT TO THE OBJECTIVE WITH EITHER OF SAID LENSES FACING SAID OBJECTIVE, AND ADJUSTMENT MEANS FOR VARYING THE RELATIVE SPACING OF SAID COMPONENTS ON SAID SUPPORT OVER A RANGE WITHIN WHICH SAID SYSTEM MAINTAINS ITS SUBSTANTIALLY AFOCAL CHARACTER WHILE HAVING A LINEAR MAGNIFICATION RATIO OF MEDIAN VALUE 1:(1+K) VARIABLE WITHIN THE LIMITS OF SAID RANGE BY A FACTOR EQUAL AT MOST TO $K, K HAVING AN ABSOLUTE VALUE OF LESS THAN 0.1 AND VARYING IN SIGN WITH THE POSITION OF SAID REVERSIBLE SUPPORT RELATIVE TO SAID OBJECTIVE, SAID DISPERSIVE COMPONENT L1 AND SAID PLANO-COLLECTIVE COMPONENT L2 HAVING RADII OF CURVATURE R1 TO R4, THICKNESSES AND VARIABLE SEPARATION D1 TO D3, REFRACTIVE INDICES ND AND ABBE NUMBERS V SUBSTANTIALLY AS GIVEN IN THE FOLLOWING TABLE: