Close focusing zoom lens

DETAILED DESCRIPTION What is claimed is: 1.
A zoom lens comprising a front focusing group of positive power movable axially, a second negative group, a third group, said second and third groups being movable axially of said lens for varying the equivalent focal length, and a fourth positive group, said first group comprising object and image side components, said components having the following relationship 2.
0>K.
sub.
12 /K.
sub.
11 >0 where K.
sub.
12 is the power of the image side component and K.
sub.
11 is the power of the object side component, and 0.
55>F.
sub.
1 /F.
sub.
L >0.
50 where F.
sub.
1 is the equivalent focal length of the first group, F.
sub.
L is the longest equivalent focal length of the lens, and said fourth group has a telephoto ratio less than 0.
9.
2.
The lens of claim 1 where said object side element of said first group is a doublet and the image side element of said first group is a singlet.
3.
The lens of claim 1 further defined as 1.
5>K.
sub.
1 /K.
sub.
M >1.
0 4.
0>.
vertline.
K.
sub.
2 /K.
sub.
M .
vertline.
>2.
2 1.
7>K.
sub.
3 /K.
sub.
M >1.
0 1.
3>K.
sub.
4 /K.
sub.
M >0.
4 where K.
sub.
1, K.
sub.
2, K.
sub.
3, and K.
sub.
4 are the powers of said first, second, third, and fourth groups, and K.
sub.
M is the geometric mean of the powers of the lens at the extremes of its focal lengths.
4.
The lens of claim 1 where said third group is a biconvex doublet.
5.
The lens of claim 1 where 2.
5K.
sub.
4 >K.
sub.
1 >1.
0K.
sub.
4 where K.
sub.
1 is the power of the first group and K.
sub.
4 is the power of the fourth group.
6.
A lens according to claim 1 wherein said second group consists of a negative singlet followed by a negative doublet.
7.
A lens according to claim 1 wherein said second group consists of a negative doublet followed by a negative singlet.
8.
A lens according to claim 2, wherein said third group consists of a biconvex doublet.
9.
A lens according to claim 1 where said fourth group comprises a positive subgroup followed by a negative subgroup with a large separating air-space