# US 2021/0278641 A1 · Attachment optical system, optical system, manufacturing method of optical system

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- Number: US 2021/0278641 A1
- Document ID: US20210278641A1
- Status: Published application
- Kind: A1
- Application number: 17/182,382
- Filed: 2021-02-23
- Published: 2021-09-09
- Earliest claimed: 2020-03-03
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Yoshiyuki Taki
- Web page: https://patentgrep.com/patent/US20210278641A1

## CPC

- G02B 9/64: having more than six components
- G02B 15/08: by changing the rear part
- G02B 3/06: with cylindrical or toric faces
- G02B 15/14: by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
- G02B 15/144511: {arranged -+-+}
- G02B 15/1461: {the first group being positive}
- G02B 15/16: with interdependent non-linearly related movements between one lens or lens group, and another lens or lens group (G02B15/22 takes precedence)
- G02B 15/167: having an additional fixed front lens or group of lenses
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An attachment optical system includes a first converter optical system attachable to an object side of an imaging optical system, and a second converter optical system attachable to an image side of the imaging optical system. The first converter optical system includes a dome-shaped cover and at least one positive lens. A predetermined condition is satisfied.

## Claims

### Claim 1

An attachment optical system comprising:
a first converter optical system attachable to an object side of an imaging optical system; and
a second converter optical system attachable to an image side of the imaging optical system,
wherein the first converter optical system includes a dome-shaped cover and at least one positive lens, and
wherein the following conditional expression is satisfied:
0.00<|fd/ffc|<0.50
where fd is a focal length of the dome-shaped cover in water, and ffc is a focal length of the at least one positive lens.

### Claim 2 (depends on 1)

The attachment optical system according to claim 1, wherein the following conditional expressions are satisfied:
5<|ffm/fwm|<50
5<|frm/fwm|<500
where ffm is a focal length of the first converter optical system in the water, fwm is a focal length of the imaging optical system in air, and frm is a focal length of the second converter optical system.

### Claim 3 (depends on 1)

The attachment optical system according to claim 1, wherein the second converter optical system includes at least one positive lens and at least one negative lens, and
wherein the following conditional expression is satisfied:
Ndp<Ndn
where Ndn is an average refractive index of the at least one negative lens in the second converter optical system, and Ndp is an average refractive index of the at least one positive lens in the second converter optical system.

### Claim 4 (depends on 1)

The attachment optical system according to claim 1, wherein the following conditional expression is satisfied:
1.00<Skcw/Skmw<1.80
where Skcw is a distance from a lens closest to an image plane in the imaging optical system to which the attachment optical system is attached, to the image plane, and Skmw is a backfocus of the imaging optical system to which the attachment optical system is not attached.

### Claim 5 (depends on 1)

The attachment optical system according to claim 1, wherein the imaging optical system does not change before and after the attachment optical system is attached to the imaging optical system.

### Claim 6

An optical system comprising:
an imaging optical system; and
an attachment optical system,
wherein the attachment optical system includes:
a first converter optical system attachable to an object side of an imaging optical system; and
a second converter optical system attachable to an image side of the imaging optical system,
wherein the first converter optical system includes a dome-shaped cover and at least one positive lens, and
wherein the following conditional expression is satisfied:
0.00<|fd/ffc|<0.50
where fd is a focal length of the dome-shaped cover in water, and ffc is a focal length of the at least one positive lens.

### Claim 7 (depends on 6)

The optical system according to claim 6, wherein the following conditional expressions are satisfied:
5<|ffm/fwm|<50
5<|frm/fwm|<500
where ffm is a focal length of the first converter optical system in the water, fwm is a focal length of the imaging optical system in air, and frm is a focal length of the second converter optical system.

### Claim 8 (depends on 6)

The optical system according to claim 6, wherein the following conditional expression is satisfied:
1.00<Skcw/Skmw<1.80
where Skcw is a distance from a lens closest to an image plane in the imaging optical system to which the attachment optical system is attached, to the image plane, and Skmw is a backfocus of the imaging optical system to which the attachment optical system is not attached.

### Claim 9 (depends on 6)

The optical system according to claim 6, wherein the following conditional expression is satisfied;
0.25≤Skmw/tdmw<1.20
where Skmw is a backfocus of the imaging optical system to which the attachment optical system is not attached, and tdmw is a distance from a lens closest to an object to a lens closest to an image plane in the imaging optical system.

### Claim 10 (depends on 6)

The optical system according to claim 6, wherein the following conditional expression is satisfied:
0.70<fwc/fwm<1.00
where fwc is a focal length of the optical system in the water, and fwm is a focal length of the imaging optical system in air.

### Claim 11

A manufacturing method of an optical system comprising the steps of:
attaching at least one positive lens in a first converter optical system to an object side of an imaging optical system;
attaching a second converter optical system to an image side of the imaging optical system; and
attaching a dome-shaped cover in the first converter optical system to the object side of the imaging optical system,
wherein the following conditional expression is satisfied:
0.0<|fd/ffc|<0.5
where fd is a focal length of the dome-shaped cover in water, and ffc is a focal length of the at least one positive lens.