Converter lens, interchangeable lens, and image capturing apparatus

Patent metadata

Field	Value
Publication number	US-12449642-B2
Application number	US-202218048216-A
Country	US
Kind code	B2
Filing date	Oct 20, 2022
Priority date	Feb 27, 2019
Publication date	Oct 21, 2025
Grant date	Oct 21, 2025

Abstract

A converter lens has negative refractive power, and is disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone. The converter lens includes a first lens element closest to an object and a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element. A focal length of the converter lens, a focal length of an air lens formed by the first lens element and the second lens element, the shape of an image-side lens surface of the first lens element, and the shape of an object-side lens surface of the second lens element are determined as appropriate.

First claim

What is claimed is:

1. A converter lens having negative refractive power and disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone, the converter lens comprising:
a first lens element closest to an object in the converter lens; and
a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
wherein a total number of positive lenses included in the converter lens is four or more, and a total number of negative lens included in the converter lens is three or more, and
wherein the following inequalities are satisfied:
1.45<| fa/f|< 8.55;
−80.0<( ra 2+ ra 1)/( ra 2− ra 1)<−2.00; and

0.15<| f 1/ f|≤ 0.520,

 where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens element, fa is a focal length of the space between the first lens element and the second lens element and is defined as fa=1/[{(1/ra1)×(1−na1)/na2}−{(1/ra2)×(1−na2)/na2}], and f1 is a focal length of the first lens element.

2. The converter lens according to claim 1 ,
wherein the converter lens includes at least one positive lens, and
wherein the following inequality is satisfied:
1.58< nAP< 1.80

 where nAP is an average d-line refractive index of a material of every positive lens included in the converter lens.

3. The converter lens according to claim 2 , wherein every lens of the converter lens is a spherical lens.

4. The converter lens according to claim 1 ,
wherein the converter lens includes at least one negative lens, and
wherein the following inequality is satisfied:
1.80< nAN< 2.20

 where nAN is an average d-line refractive index of a material of every negative lens included in the converter lens.

5. The converter lens according to claim 4 , wherein every lens of the converter lens is a spherical lens.

6. The converter lens according to claim 1 ,
wherein the following inequality is satisfied:
0.01<| f 1/ fa|< 0.40

 where f1 is a focal length of the first lens element.

7. The converter lens according to claim 6 , wherein every lens of the converter lens is a spherical lens.

8. The converter lens according to claim 1 ,
wherein the following inequality is satisfied:
30.0< νAN< 39.0,

 where νAN is an average Abbe number of a material of every negative lens included in the converter lens.

9. The converter lens according to claim 8 , wherein every lens of the converter lens is a spherical lens.

10. The converter lens according to claim 1 ,
wherein a lens surface closest to an image in the converter lens is convex with respect to the image, and
wherein the following inequality is satisfied:
0.02< rl/f< 0.32

 where rl is a curvature radius of the lens surface.

11. The converter lens according to claim 1 ,
wherein the converter lens includes at least one positive lens, and
wherein the following inequality is satisfied:
1.75< nd 1<2.00

 where nd1 is a d-line refractive index of the positive lens closest to the object among the positive lens included in the converter lens.

12. The converter lens according to claim 1 ,
wherein the first lens element has positive refractive power, and the second lens element has negative refractive power, and
wherein the following inequality is satisfied:
0.04< f 2/ f< 1.10

 where f2 is a focal length of the second lens element.

13. The converter lens according to claim 1 , wherein the following inequality is satisfied:
1.00< ra 2/ rl< 3.40
where rl is a curvature radius of an image-side lens surface of a lens closest to an image in the converter lens.

14. The converter lens according to claim 1 , wherein the second lens element includes a cemented lens including a negative lens, a positive lens, and a negative lens in this order from an object side to an image side.

15. The converter lens according to claim 1 , wherein the object-side lens surface of the second lens element is concave with respect to the object.

16. The converter lens according to claim 1 , wherein an image-side lens surface of the second lens element is concave with respect to an image.

17. The converter lens according to claim 1 , wherein a lens element closest to an image in the converter lens has positive refractive power.

18. The converter lens according to claim 1 , wherein every lens of the converter lens is a spherical lens.

19. An interchangeable lens comprising a master lens and a converter lens having negative refractive power and configured to be inserted to or removed from an optical path of the master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone, the converter lens comprising:
a first lens element closest to an object in the converter lens; and
a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
wherein a total number of positive lenses included in the converter lens is four or more, and a total number of negative lens included in the converter lens is three or more, and
wherein the following inequalities are satisfied:
1.45<| fa/f|< 8.55;
−80.0<( ra 2+ ra 1)/( ra 2− ra 1)<−2.00; and

0.15<| f 1/ f|≤ 0.520,

 where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens element, fa is a focal length of the space between the first lens element and the second lens element and is defined as fa=1/[{(1/ra1)×(1−na1)/na2}−{(1/ra2)×(1−na2)/na2}], and f1 is a focal length of the first lens element.

20. An image capturing apparatus comprising:
a master lens;
a converter lens having negative refractive power and disposed on an optical path of the master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone; and
an image sensor,
the converter lens comprising:
a first lens element closest to an object in the converter lens; and
a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element,
wherein a total number of positive lenses included in the converter lens is four or more, and a total number of negative lens included in the converter lens is three or more, and
wherein the following inequalities are satisfied:
1.45<| fa/f|< 8.55;
−80.0<( ra 2+ ra 1)/( ra 2− ra 1)<−2.00; and

0.15<| f 1/ f|≤ 0.520,

 where f is a focal length of the converter lens, na1 is a d-line refractive index of a material of an image-side lens of the first lens element, na2 is a d-line refractive index of a material of an object-side lens of the second lens element, ra1 is a curvature radius of the image-side lens surface of the first lens element, ra2 is a curvature radius of the object-side lens surface of the second lens e

Assignees

• Canon Kk

Inventors

• Saito Shinichiro
• Ebe Hiroki

Classifications

• G02B15/12

  by adding telescopic attachments (G02B15/14 takes precedence) · CPC title

• G03B17/14 Primary

  interchangeably · CPC title

• G02B7/021

  for more than one lens · CPC title

• G02B27/0025

  for optical correction, e.g. distorsion, aberration · CPC title

• G03B17/58

  Attachments for converting cameras into reflex cameras · CPC title