# US 11,307,330 B2 · Variable focal length optical system

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- Number: US 11,307,330 B2
- Document ID: US11307330B2
- Status: Granted
- Kind: B2
- Application number: 17/148,998
- Filed: 2021-01-14
- Published: 2021-07-22
- Granted: 2022-04-19
- Earliest claimed: 2020-01-20
- Assignees: Mitutoyo Corporation
- Applicants: Mitutoyo Corporation
- Inventors: Koji Kubo; Yuko Shishido
- Web page: https://patentgrep.com/patent/US11307330B2

## CPC

- G02B 3/14: of variable focal length
- G02B 21/367: {providing an output produced by processing a plurality of individual source images, e.g. image tiling, montage, composite images, depth sectioning, image comparison}
- G02B 13/0095: {Relay lenses or rod lenses (in instruments for viewing the inside of hollow bodies G02B23/2446)}
- G02B 21/02: Objectives
- G02B 26/004: {based on a displacement or a deformation of a fluid}
- G02B 7/04: with mechanism for focusing or varying magnification
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A variable focal length optical system includes: an imaging lens configured to condense a parallel beam of light from an objective lens to form an intermediate image; a relay system including, in sequence from an object side, a first relay lens and a second relay lens and configured to relay the intermediate image to infinity; and a lens system of a liquid resonant type which is located between the first relay lens and the second relay lens. A front principal point of the lens system is located to be conjugated with an exit pupil of the objective lens and an expression, 1.90≤fTube/fR1≤2.15, is satisfied. In the expression, fTube denotes a focal length of the imaging lens and fR1 denote a focal length of the first relay lens.

## Claims

### Claim 1

A variable focal length optical system used in combination with an infinity corrected objective lens, the variable focal length optical system comprising:
an imaging lens configured to condense a parallel beam of light from the objective lens to form an intermediate image;
a relay system comprising, in sequence from an object side, a first relay lens and a second relay lens, the relay system configured to relay the intermediate image to infinity; and
a lens system of a liquid resonant type which is located between the first relay lens and the second relay lens, the lens system having a refractive index that changes in response to an inputted drive signal, wherein
a front principal point of the lens system is located to be conjugated with an exit pupil of the objective lens, and
with fTube denoting a focal length of the imaging lens and fR1 denoting a focal length of the first relay lens, an expression (1) below is satisfied,
1.90<fTube/fR1≤2.15 (1).

### Claim 2 (depends on 1)

The variable focal length optical system according to claim 1, wherein
with X denoting a distance from a front end surface of the lens system to the front principal point of the lens system, an expression (2) below is satisfied,
X<fR1≤2X (2).

### Claim 3 (depends on 1)

The variable focal length optical system according to claim 1, wherein
with fR2 denoting a focal length of the second relay lens and fobj1x denoting a focal length of the objective lens with 1× magnification, an expression (3) below is satisfied,
fR2=fobj1x×fR1/fTube (3).