Zoom lens having close-up focusing mode of operation

Claim 2

A lens having a first front focusing lens group of positive power, a second zoom lens group of negative power, a third compensating lens group of negative power, and a fourth fixed objective of positive power from the front to back, said zoom group and said compensating group being movable axially in a first mode in a predetermined nonlinear relation to vary the equivalent focal length of said lens, and said zoom and compensating groups being movable together axially and equally in a second mode for close focusing.

Claim 3

The lens of claim 1 wherein said first group is a three element construction L1, L2, L3, comprising a convex-concave and double convex cemented doublet, and a single convex-concave lens; said second group is a three element construction L4, L5, L6 comprising a double convex, double concave cemented doublet and a double-concave single element; said third group is a two element construction L7, L8 comprising a double concave, convex-concave cemented doublet; and the fourth group is a seven element telephoto objective comprising a double convex, concave-convex cemented doublet L9, L10, a single convex-concave element L11, a double convex-double concave cemented doublet L12, L13, a concave-convex single element L14, and a double convex single element L15; where L1-L15 are the lens elements successively from the object to the film plane.

Claim 4

The lens of claim 2 wherein the axial distance of element L1 from the subject surface thereof to the film plane surface of L15 measured along the axis of the lens is less than the maximum equivalent focal length of the lens.

Claim 5

The lens of claim 2 wherein the dispersion of element L10 referenced by its Abbe number is 26.0 or greater.

Claim 6

The lens of claim 4 wherein the elements L9, L11 and L12 have indices of refraction of less than 1.52.

Claim 7

The lens of claim 1 wherein 0.45 F1 < or = F2 < or = 0.55F1 and F4 < or = 0.3F1 where F1, and F2 and F3 are the equivalent focal lengths of the first, and second and third lens groups respectively, and F4 is the combined equivalent focal length of the second and third lens groups when positioned for close-up focusing.

Claim 8

The lens of claom 1 wherein said first group is a three element construction L1, L2, L3; said second group is a three element construction L4, L5, L6; said third group is a two element construction L7, L8; and the fourth group is a telephoto objective where L1-L8 are the lens elements successively from the object counted toward the film plane.

Claim 9

The lens of claom 1 wherein said first group is a three element construction L1, L2, L3; said second group is a three element construction L4, L5, L6; said third group is a two element construction L7, L8; and the fourth group is a telephoto objective where L1-L8 are the lens elements successively from the object counted toward the film plane.

Claim 10

The lens of claim 7 wherein 0.4F3 < or = f7 < or = 0.5F3 and 0.55F3 < or = r11 < or = 0.6F3 where F3 is the equivalent focal length of said third lens group, f7 is the equivalent focal length of element L7 and r11 is the radius of curvature of the front surface of element L7.

Claim 11

The lens of claim 7 wherein the difference in the dispersions of lens element L7 and L8 as referenced to their Abbe numbers is greater than 23.0.

Claim 12

The lens of claim 7 having the following characteristics:

Claim 13

The lens of claim 1 having the following characteristics where said first group comprises elements L1, L2, L3; said second group comprises elements L4, L5, L6; said third group comprises elements L7, L8; and said fourth group comprises elements L9-L15.