Three element objective lens

Claim 2

A three element objective lens comprising, from front to rear, a positive meniscus element, a negative biconcave element and a positive biconvex element, each of said elements being formed of a glass having an index of refraction in excess of 1.90 and said lens including an aspheric surface on the rear surfaces of said positive meniscus element and said negative biconcave element, said aspheric surfaces being represented by the following formula and parameters: ##EQU2## Surface R=1/C K D ______________________________________ 2 36.338 0 0.12283 × 10.sup..sup.-3 4 9.4853 -1.6218 0 ______________________________________ wherein x is the sag of the aspheric surface from a plane reference surface at a radial distance y from the axis of the lens, C is equal to the reciprocal of the vertex radius of curvature R and K is the conic constant.

Claim 3

A three element objective lens comprising, from front to rear, a positive meniscus element, a negative biconcave element and a positive biconvex element, each of said elements being formed of a glass having an index of refraction in excess of 1.90 and said lens including an aspheric surface on the rear surfaces of said positive meniscus element and said negative biconcave element, said lens having a focal length of 25.00mm when constructed according to the parameters in the following table: Radius Thickness or Element N V mm Separation mm ______________________________________ R.sub.1 =13.506 1 2.01940 34.21 T.sub.1 =6.000 R.sub.2 =Asphere R.sub.3 =-185.19 S.sub.1 =1.210 2 1.90893 19.31 T.sub.2 =1.200 R.sub.4 =Asphere R.sub.5 =25.258 S.sub.2 =1.340 3 2.01940 34.21 T.sub.3 =6.000 R.sub.6 =-25.258 S.sub.3 =.500 ______________________________________ wherein, from front to rear, the elements are numbered from 1 to 3, the corresponding indices of refraction, N, and Abbe' numbers, V, are listed for each of the lens elements, the radii are numbered from R 1 to R 6 , the thicknesses are numbered from T 1 to T 3 and the air spaces are numbered from S 1 to S 3 , and wherein R 2 and R 4 represent the radius of curvature at the vertex of aspheric surfaces defined by the following formula and parameters: ##EQU3## Surface R=1/C K D ______________________________________ 2 36.338 0 0.12283 × 10.sup..sup.-3 4 9.4853 -1.6218 0 ______________________________________ wherein X is the sag of the aspheric surface from a plane reference surface at a radial distance y from the axis of the lens, C is equal to the reciprocal of the vertex radius R and K is the conic constant.

Claim 4

A three element objective lens comprising, from front to rear, a positive meniscus element, a negative biconcave element and a positive biconvex element, each of said elements being formed of a glass having an index of refraction in excess of 1.90 and said lens including an aspheric surface on the rear surfaces of said positive meniscus element and said negative biconcave element, said lens having a focal length of 25.00mm when constructed according to the parameters in the following table: Radius Thickness or Element N V mm Separation mm ______________________________________ R.sub.1 =13.506 1 2.01940 34.21 T.sub.1 =6.000 R.sub.2 =Asphere R.sub.3 =-185.19 S.sub.1 =1.210 2 1.90893 19.31 T.sub.2 =1.200 R.sub.4 =Asphere R.sub.5 =25.258 S.sub.2 =1.340 3 2.01940 34.21 T.sub.3 =6.000 R.sub.6 =-25.258 S.sub.3 =.500 ______________________________________ wherein, from front to rear, the elements are numbered from 1 to 3, the corresponding indices of refraction, N, and Abbe' numbers, V, are listed for each of the lens elements, the radii are numbered from R 1 to R 6 , the thicknesses are numbered from T 1 to T 3 and the air spaces are numbered from S 1 to S 3 , and wherein R 2 and R 4 represent the radius of curvature at the vertex of aspheric surfaces defined by the following formula and parameters: ##EQU3## Surface R=1/C K D ______________________________________ 2 36.338 0 0.12283 × 10.sup..sup.-3 4 9.4853 -1.6218 0 ______________________________________ wherein X is the sag of the aspheric surface from a plane reference surface at a radial distance y from the axis of the lens, C is equal to the reciprocal of the vertex radius R and K is the conic constant.