Converter lens, interchangeable lens, and image-capturing apparatus

Patent metadata

Field	Value
Publication number	US-11428910-B2
Application number	US-202017092373-A
Country	US
Kind code	B2
Filing date	Nov 9, 2020
Priority date	Nov 14, 2019
Publication date	Aug 30, 2022
Grant date	Aug 30, 2022

Abstract

A converter lens (RCL) has a negative refractive power, which is disposed on an image side of a master lens (ML) to make a focal length of an entire system longer than that of the master lens alone. The converter lens comprises a most image-side lens element (LT) disposed closest to an image side in the converter lens, wherein the most image-side lens element has a lens surface having a convex shape toward an image side, a lens disposed closest to an image side in the converter lens has a positive refractive power, and mN<mP and 0.0≤LR 2 /AR 2 <1.0 are satisfied.

First claim

What is claimed is:

1. A converter lens having a negative refractive power, which is disposed on an image side of a master lens to make a focal length of an entire system longer than a focal length of the master lens alone, the converter lens comprising:
a most image-side lens element disposed closest to an image side in the converter lens,
wherein the most image-side lens element has a lens surface having a convex shape toward an image side,
wherein a lens disposed closest to an image side in the converter lens has a positive refractive power, and
wherein the following conditional expressions are satisfied:
mN<mP
0.0≤ LR 2/ AR 2<1.0

where mP is the number of positive lens components of the converter lens, mN is the number of negative lens components of the converter lens, LR 2 is a radius of curvature of an image-side lens surface of the most image-side lens element, and AR 2 is a radius of curvature of an object-side lens surface of the most image-side lens element.

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

where nAP is an average refractive index at a d line of materials of all positive lenses included in the converter lens.

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

where nAN is an average refractive index at a d line of materials of all negative lenses included in the converter lens.

4. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.0≤ LR 2/ AR 1<0.9

where AR 1 is a radius of curvature of an image-side lens surface of the lens element adjacent to an object side of the most image-side lens element.

5. The converter lens according to claim 1 ,
wherein the most image-side lens element includes a single lens having a positive refractive power, which is disposed closest to an image side, and
wherein the following conditional expression is satisfied:
0.05<| fLP/f|< 0.60

where fLP is a focal length of the single lens and f is a focal length of the converter lens.

6. The converter lens according to claim 1 ,
wherein the most image-side lens element includes a single lens having a positive refractive power, which is disposed closest to an image side, and
wherein the following conditional expression is satisfied:
1.45< nLP< 1.75

where nLP is an average refractive index at a d line of materials of the single lens.

7. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.0≤ LR 2/ BR 2<1.0

where BR 2 is a radius of curvature of an object-side lens surface of the lens element adjacent to an object side of the most image-side lens element.

8. The converter lens according to claim 1 , further comprising:
a lens element adjacent to an object side of the most image-side lens element,
wherein the following conditional expression is satisfied:
0.4< AR 2/ AR 1<2.0

where AR 1 is a radius of curvature of an image-side lens surface of the lens element adjacent to an object side of the most image-side lens element.

9. The converter lens according to claim 1 ,
wherein the following conditional expression is satisfied:
−7.0< SFL<− 1.0

where SFL is a shape factor of the most image-side lens element.

10. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens,
wherein the following conditional expression is satisfied:
0.1<| fl/f|< 0.9

where fl is a focal length of the most object-side lens element and f is a focal length of the converter lens.

11. The converter lens according to claim 1 , further comprising:
a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented in order from an object side to an image side.

12. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens; and
a lens element adjacent to an image side of the most object-side lens element,
wherein an object-side lens surface of the lens element adjacent to an image side of the most object-side lens element is concave toward an object side.

13. The converter lens according to claim 1 , further comprising:
a most object-side lens element disposed closest to an object side in the converter lens; and
a lens element adjacent to an image side of the most object-side lens element,
wherein an image-side lens surface of the lens element adjacent to an image side of the most object-side lens element is concave toward an image side.

14. The converter lens according to claim 1 ,
wherein the most image-side lens element has a positive refractive power.

15. The converter lens according to claim 1 ,
wherein all lenses that compose the converter lens are spherical lenses.

16. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens and a positive lens are cemented, a third lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, and a fourth lens element which is a positive single lens.

17. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a cemented lens in which a positive lens and a negative lens are cemented, and a fourth lens element which is a positive single lens.

18. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a positive single lens, and a fourth lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, and a fifth lens element which is a positive single lens.

19. The converter lens according to claim 1 ,
wherein the converter lens consists of, in order from an object side to an image side, a first lens element which is a positive single lens, a second lens element which is a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, a third lens element which is a positive single lens, a fourth lens element which is a cemented lens in which a negative lens and a positive lens are cemented, and a fifth lens element which is a cemented lens in which a negative lens and a positive lens are cemented.

20. An interchangeable lens comprising:
a master lens; and
a converter lens having a negative refractive power, which is disposed on

Assignees

• Canon Kk

Inventors

• Saito Shinichiro
• Ebe Hiroki

Classifications

• G02B13/006

  at least one element being a compound optical element, e.g. cemented elements · CPC title

• G02B13/005 Primary

  having spherical lenses only · CPC title

• G02B15/10

  by adding a part, e.g. close-up attachment · CPC title

• G02B7/14

  adapted to interchange lenses {(G02B7/027 takes precedence)} · CPC title

• G02B13/16 Primary

  for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV} · CPC title