# US 6,724,547 B2 · Single-focus lens

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- Number: US 6,724,547 B2
- Document ID: US6724547B2
- Status: Granted
- Kind: B2
- Application number: 10/280,053
- Filed: 2002-10-25
- Published: 2003-05-22
- Granted: 2004-04-20
- Earliest claimed: 2001-11-16
- Assignees: Fuji Photo Optical Co., Ltd.
- Inventors: Kenichi Sato
- Web page: https://patentgrep.com/patent/US6724547B2

## CPC

- G02B 9/16: all the components being simple
- G02B 13/0035: {having three lenses}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A single-focus lens includes from the object side, a first lens with a positive refracting power having at least one aspheric surface, a stop, a second lens with a negative refracting power, and a third lens with a positive refracting power having at least one aspheric surface. This single-focus lens further satisfies the conditional expression of 0.3<f/f2′3<0.8, where f is the focal length of the lens as a whole, and f23 is the composite focal length of the second and third lenses.

## Claims

### Claim 1

A single-focus lens comprising, successively from the object side, a first lens with a positive refracting power having at least one aspheric surface, a stop, a second lens with a negative refracting power, and a third lens with a positive refracting power having at least one aspheric surface; and satisfying the following conditional expression (1):
0.3f′/f′23<0.8 (1)
where
f′ is the focal length of the lens as a whole; and
f′23 is the composite focal length of the second and third lenses.

### Claim 2 (depends on 1)

A single-focus lens according to claim 1, wherein said first lens has a meniscus form with a concave surface on the object side, said second lens has a concave surface on the object side, and said third lens has a convex surface on the image surface side; said single-focus lens satisfying the following conditional expression (2):
2.0<|R11+R12|/|R11−R12|<8.0 (2)
where
R11 is the radius of curvature of the object-side surface of the first lens;
and
R12 is the radius of curvature of the image-surface-side surface of the first lens.

### Claim 3 (depends on 1)

A single-focus lens according to claim 1, wherein said single-focus lens satisfies the following conditional expressions (3) to (6):
1.70<Nd1 (3)
1.60<Nd3 (4)
35>νd1 (5)
40<νd3 (6)
where
Nd1 is the refractive index of the first lens at d-line;
Nd3 is the refractive index of the third lens at d-line;
νd1 is the Abbe number of the first lens at d-line; and
νd3 is the Abbe number of the third lens at d-line.

### Claim 4 (depends on 1)

A single-focus lens according to claim 1, wherein said single-focus lens is mounted in a collapsible camera, said first, second, and third lenses being integrally moved on an optical axis so as to shorten a distance between said third lens and an imaging device when said camera collapses.

### Claim 5 (depends on 1)

A single-focus lens according to claim 1, wherein at least one of lens surfaces of said first, second, and third lenses is provided with a coating having a function of a low-pass filter and/or an infrared cut filter.