# US 5,353,160 A · Three-unit compact zoom lens system

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- Number: US 5,353,160 A
- Document ID: US5353160A
- Status: Granted
- Kind: A
- Application number: 07/917,999
- Filed: 1992-07-24
- Granted: 1994-10-04
- Earliest claimed: 1991-07-24
- Assignees: Olympus Optical Co., Ltd.
- Inventors: Yasuji Ogata
- Web page: https://patentgrep.com/patent/US5353160A

## CPC

- G02B 15/143103: {arranged ++-}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The present invention provides a three-unit zoom lens system comprising, in order from the object side, a first lens unit G1 consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and having a positive refracting power as a whole, a second lens unit G2 consisting of one positive lens, or one negative lens and one positive lens, and having a positive refracting power as a whole and a third lens unit G3 consisting of one negative lens, said first and second lens units being movable toward each other for zooming from the wide to tele position. This compact zoom lens system comprises 4 or 5 lenses and is of sufficient performance in terms of a zoom ratio of 1.5 to 2.

## Claims

### Claim 1

A zoom lens system comprising in order from the object side;
a first lens unit consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and having a positive refracting power as a whole,
a second lens unit including one positive lens, or one negative lens and one positive lens, and having a positive refracting power as a whole, and
a third lens unit consisting of one negative lens,
said first and second lens units being movable toward each other for zooming from the wide to tele position.

### Claim 2 (depends on 1)

A zoom lens system as claimed in claim 1, wherein an aspherical surface is incorporated in said second lens unit.

### Claim 3 (depends on 1)

A zoom lens system as claimed in claim 1, wherein an aspherical surface is incorporated in said third lens unit.

### Claim 4 (depends on 1, 2, 3)

A zoom lens system as claimed in claim 1, 2 or 3, which conforms to the following conditions (1) and (2):
0.5<.vertline.f.sub.3 /f.sub.W .vertline.<1.2, (1) and
1.2<.beta..sub.3W <1.8, (2)
where
f.sub.W is the focal length of the total system at the wide position,
f.sub.3 is the focal length of said third lens unit, and
.beta..sub.3W is the image-formation magnification of said third lens unit at the wide position.

### Claim 5 (depends on 1, 2, 3)

A zoom lens system as claimed in claim 1, 2 or 3, which conforms to the following condition (3):
0.5<f.sub.2 /f.sub.W <1.3, (3)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 6 (depends on 4)

A zoom lens system as claimed in claim 4, which conforms to the following condition (4):
0.5<f.sub.2 /f.sub.W <1.3, (4)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 7 (depends on 1, 2, 3)

A zoom lens system as claimed in claim 1, 2 or 3, which conforms to the following conditions (5) and (6):
0.7<(r.sub.a +r.sub.b)/(r.sub.a -r.sub.b)<3, (5) and
0.12<L/f.sub.W <0.3, (6)
where
r.sub.a and r.sub.b are the object- and image-side radii of curvature of the positive lens in said second lens unit, respectively, and
L is the distance of said second lens from the stop to the object side of the positive lens.

### Claim 8 (depends on 1)

A zoom lens system as claimed in claim 1, wherein said second and third lens units are movable to decrease a separation between said second and third lens units for zooming from the wide to tele position.

### Claim 9

A zoom lens system comprising in order from the object side:
a first lens unit consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and having a positive refracting power as a whole,
a second lens unit consisting of one positive lens, and having a positive refracting power as a whole, and
a third lens unit consisting of one negative lens,
said first and second lens units being movable to increase a separation between said first and second lens units for zooming from the wide to tele position.

### Claim 10 (depends on 9)

A zoom lens system as claimed in claim 9, wherein an aspherical surface is incorporated in said second lens unit.

### Claim 11 (depends on 9)

A zoom lens system as claimed in claim 9, wherein an aspherical surface is incorporated in said third lens unit.

### Claim 12 (depends on 9, 10, 11)

A zoom lens system as claimed in claim 9, 10 or 11, which conforms to the following conditions (1) and (2):
0.5<.vertline.f.sub.3 /f.sub.W .vertline.<1.2, (1)
1.2<.beta..sub.3W <1.8 (2)
where
f.sub.W is the focal length of the total system at the wide position,
f.sub.3 is the focal length of said third lens unit, and
.beta..sub.3W is the image-formation magnification of said third lens unit at the wide position.

### Claim 13 (depends on 9, 10, 11)

A zoom lens system as claimed in claim 9, 10 or 11, which conforms to the following condition (3):
0.5<f.sub.2 /f.sub.W <1.3 (3)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 14 (depends on 12)

A zoom lens system as claimed in claim 12, which conforms to the following condition (4):
0.5<f.sub.2 /f.sub.W <1.3 (4)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 15 (depends on 9, 10, 11)

A zoom lens system as claimed in claim 9, 10 or 11, which conforms to the following conditions (5) and (6):
0.7<(r.sub.a +r.sub.b)/(r.sub.a -r.sub.b) <3 (5)
0.12<L/f.sub.W <0.3 (6)
where
r.sub.a and r.sub.b are the object- and image-side radii of curvature of the positive lens in said second lens unit, respectively, and
L is the distance of said second lens unit from the stop to the object side of the positive lens.

### Claim 16

A zoom lens system comprising in order from the object side:
a first lens unit consisting of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side and having a positive refracting power as a whole,
a second lens unit consisting of one negative lens and one positive lens, and having a positive refracting power as a whole, and
a third lens unit consisting of one negative lens,
said first and second lens units being movable to increase a separation between said first and second lens units for zooming from the wide to tele position.

### Claim 17 (depends on 16)

A zoom lens system as claimed in claim 16, wherein an aspherical surface is incorporated in said second lens unit.

### Claim 18 (depends on 16)

A zoom lens system as claimed in claim 16, wherein an aspherical surface is incorporated in said third lens unit.

### Claim 19 (depends on 16, 17, 18)

A zoom lens system as claimed in claim 16, 17 or 18, which conforms to the following conditions (1) and (2):
0.5<.vertline.f.sub.3 /f.sub.W .vertline.<1.2, (1)
1.2<.beta..sub.3W <1.8 (2)
where
f.sub.W is the focal length of the total system at the wide position,
f.sub.3 is the focal length of said third lens unit, and
.beta..sub.3W is the image-formation magnification of said third lens unit at the wide position.

### Claim 20 (depends on 16, 17, 18)

A zoom lens system as claimed in claim 16, 17 or 18, which conforms to the following condition (3):
0-5<f.sub.2 /f.sub.W <1.3 (3)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 21 (depends on 19)

A zoom lens system as claimed in claim 19, which conforms to the following condition (4):
0.5<f.sub.2 /f.sub.W <1.3 (4)
where
f.sub.W is the focal length of the total system at the wide position, and
f.sub.2 is the focal length of said second lens unit.

### Claim 22 (depends on 16, 17, 18)

A zoom lens system as claimed in claim 16, 17 or 18, which conforms to the following conditions (5) and (6):
0.7<(r.sub.a +r.sub.b)/(r.sub.a -r.sub.b)<3 (5)
0.12<L/f.sub.W <0.3 (6)
where
r.sub.a and r.sub.b are the object- and image-side radii of curvature of the positive lens in said second lens unit, respectively, and
L is the distance of said second lens unit from the stop to the object side of the positive lens.