# US 2019/0171000 A1 · Eyepiece optical system and observation apparatus

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2019/0171000 A1
- Document ID: US20190171000A1
- Status: Published application
- Kind: A1
- Application number: 16/203,871
- Filed: 2018-11-29
- Published: 2019-06-06
- Earliest claimed: 2017-12-01
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Ai Takumi
- Web page: https://patentgrep.com/patent/US20190171000A1

## CPC

- G02B 25/001: {Eyepieces}
- G02B 9/14: arranged + - +
- G02B 9/34: having four components only
- G02B 23/14: Viewfinders (for photographic apparatus G03B13/02)
- G02B 27/0031: {for scanning purposes}
- H04N 23/63: by using electronic viewfinders
- H04N 23/53: of electronic viewfinders, e.g. rotatable or detachable
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

The present invention provides an eyepiece optical system for observing an image displayed on an image display surface. The eyepiece optical system includes a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, which are arranged in this order from an image display surface side to an observation side. A focal length of the first lens, a focal length of the third lens, a curvature radius of a lens surface on the observation side of the first lens, and a curvature radius of a lens surface on the image display surface side of the second lens are appropriately set.

## Claims

### Claim 1

An eyepiece optical system for observing an image displayed on an image display surface, the eyepiece optical system comprising:
a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power arranged in this order from an image display surface side to an observation side, wherein
the following conditional expressions are satisfied:
0.450≤f1/f3≤0.880; and
0.160<(L2R1−L1R2)/(L2R1+L1R2)≤0.294
where f1 represents a focal length of the first lens, f3 represents a focal length of the third lens, L1R2 represents a curvature radius of a lens surface on the observation side of the first lens, and L2R1 represents a curvature radius of a lens surface on the image display surface side of the second lens.

### Claim 2 (depends on 1)

The eyepiece optical system according to claim 1, wherein the following conditional expression is satisfied:
0.00≤d5/d3≤2.00
where d3 represents an interval on an optical axis between the first lens and the second lens and d5 represents an interval on the optical axis between the second lens and the third lens.

### Claim 3 (depends on 1)

The eyepiece optical system according to claim 1, further comprising:
a fourth lens having a positive or negative refractive power and being arranged on the observation side of the third lens.

### Claim 4 (depends on 1)

The eyepiece optical system according to claim 1, wherein the first lens has a biconvex shape.

### Claim 5 (depends on 1)

The eyepiece optical system according to claim 1, wherein the lens surface on the image display surface side of the second lens has a concave shape.

### Claim 6 (depends on 1)

The eyepiece optical system according to claim 1, wherein the third lens has a biconvex shape.

### Claim 7

An observation apparatus comprising:
an image display element configured to display an image; and
an eyepiece optical system used to observe an image displayed on an image display surface of the image display element, wherein
the eyepiece optical system includes a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power arranged in this order from the image display surface of the image display element to an observation side, and
the following conditional expressions are satisfied:
0.450≤f1/f3≤0.880; and
0.160<(L2R1−L1R2)/(L2R1+L1R2)≤0.294
where f1 represents a focal length of the first lens, f3 represents a focal length of the third lens, L1R2 represents a curvature radius of a lens surface on the observation side of the first lens, and L2R1 represents a curvature radius of a lens surface facing on the image display surface of the second lens.

### Claim 8 (depends on 7)

The observation apparatus according to claim 7, wherein the following conditional expression is satisfied:
0.25<PN/f<0.55
where PN represents a half diagonal length of the image display surface of the image display element.