# US 4,398,807 A · Zoom lens

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- Number: US 4,398,807 A
- Document ID: US4398807A
- Status: Granted
- Kind: A
- Application number: 06/235,086
- Filed: 1981-02-17
- Granted: 1983-08-16
- Earliest claimed: 1980-02-26
- Assignees: Nippon Kogaku K. K.
- Inventors: Yutaka Iizuka
- Web page: https://patentgrep.com/patent/US4398807A

## CPC

- G02B 15/144113: {arranged +-++}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An improvement in zoom lenses of the type consisting of four lens groups of positive, negative, positive, power positive and arranged in this order as viewed from the object side is disclosed. The improved zoom lenses exhibit excellent high focusing ability even for close distance photographing with higher magnification.

## Claims

### Claim 1

In a zoom lens consisting of a first positive lens group, a second negative lens group, a third positive lens group and a fourth positive lens group arranged in this order as viewed from the object field side, wherein the first lens group functions as a focusing unit, the second lens group functions as a variator for changing the magnification by moving along the optical axis in a linear fashion, the third lens group functions as a compensator for maintaining at a predetermined position the image plane which is variable with the movement of said second lens group, and the fourth lens group functions as a relay lens, and wherein said first lens group is composed of a front component constitututed by a positive lens and a rear component constituted by a positive lens and a negative lens cemented together with the resulting power being positive and the cemented surface being concave toward the object side, the improvement being characterized in that said zoom lens satisfies the following conditions: ##EQU4## wherein, f1, f2, f3 and f4 are the focal lengths of said first, second, third and fourth lens groups, respectively;
fW is the shortest focal length of the total system offered by zooming;
fT is the longest focal length thereof;
f1F is the focal length of the front component of said first lens group;
f1R is the focal length of the rear component thereof;
r1 and r2 are radii of curvature of the first and second surfaces of said front component, respectively, r4 is the radius of curvature of the cemented surface of said rear component of the first lens group, and r3 and r5 are radii of curvature of the surfaces at the object side and at the image side of said rear component, respectively; and n2 is the refractive index of the positive lens constituting said rear component of the first lens group and n3 is the refractive index of the negative lens constituting said rear component of the first lens group.

### Claim 2 (depends on 1)

A zoom lens as set forth in claim 1 which is characterized by the following data:
focal length f=75.024.about.106.106.about.150.086 F number 3.5
______________________________________ r d nd .nu.d ______________________________________ 1 120.600 5.1000 1.62041 60.3 2 -262.500 0.2000 3 98.380 5.7000 1.62041 60.3 4 -173.840 1.6000 1.75520 27.5 5 215.500 d5 = variable 6 -163.222 3.7000 1.78470 26.1 7 -40.083 1.2000 1.51680 64.2 8 54.000 3.8000 9 -42.000 1.2000 1.62041 60.3 10 124.706 d10 = variable 11 135.900 5.3000 1.62041 60.3 12 -30.776 1.1000 1.75520 27.5 13 -66.990 d13 = variable 14 33.750 4.7000 1.62041 60.3 15 133.032 1.0000 16 -462.320 2.1000 1.75520 27.5 17 637.000 42.0 18 -19.704 2.0000 1.74950 34.96 19 -28.653 0.3000 20 77.683 3.9000 1.62588 35.6 21 -419.799 ______________________________________ f1 = 103.016 f1F = 133.877 f2 = -35.355 f1R = 467.476 f3 = 88.074 B.f = 40.165 f4 = 95.281 ______________________________________ f 75.024 106.106 150.086 d5 1.850 17.227 28.101 d10 24.364 14.502 0.555 d13 8.146 2.631 5.706 ______________________________________
wherein,
r is radius of curvature of lens surface;
d is lens thickness or space at center;
nd is refractive index of lens;
.nu.d is Abbe number of lens; and
the number given in the left-most column indicates the order of lens surfaces as viewed from the object field side.