Lens system and imaging apparatus

Patent metadata

Field	Value
Publication number	US-11867889-B2
Application number	US-201917252803-A
Country	US
Kind code	B2
Filing date	Jun 18, 2019
Priority date	Jun 19, 2018
Publication date	Jan 9, 2024
Grant date	Jan 9, 2024

Abstract

A lens system for imaging includes, in order from the object side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, a stop, and a fourth lens group with positive refractive power. The third lens group includes, closest to the image plane side, a cemented lens on the object side of the stop and whose image plane-side surface includes a concave surface on the object side. The fourth lens group includes, closest to the object side, a cemented lens on the image plane side of the stop and whose object-side surface includes a concave surface on the image plane side. A radius of curvature g3er of the object side concave surface and the radius of curvature g4fr of the image plane side concave surface satisfy the following condition: 2.5≤|g4fr/g3er|≤4.0.

First claim

The invention claimed is:

1. A lens system for imaging consisting, in order from an object side, of a first lens group that has negative refractive power, a second lens group that has positive refractive power, a third lens group that has positive refractive power, a stop, and a fourth lens group that has positive refractive power,
wherein the third lens group includes, at a position closest to an image plane side, a cemented lens disposed on the object side of the stop and including an image plane side-surface with a surface that is concave on the object side,
the fourth lens group includes, at a position closest to the object side, a cemented lens disposed closest to the image plane side of the stop and including an object side surface with a surface that is concave on the image plane side, and
the cemented lens disposed on the object side of the stop and the cemented lens disposed on the image plane side of the stop have negative refractive powers,
a radius of curvature g 3 er of the surface that is concave on the object side, a radius of curvature g 4 fr of the surface that is concave on the image surface side, a focal length B 2 f of the cemented lens disposed on the object side of the stop and a focal length B 3 f of the cemented lens disposed on the image plane side of the stop satisfy following conditions:
2.5≤| g 4 fr/g 3 er|≤ 4.0, and

1.7≤ B 3 f/B 2 f≤ 3.0.

2. An imaging apparatus comprising:
a lens system according to claim 1 ; and
an imaging element disposed on the image plane side of the lens system.

3. The lens system according to claim 1 , A lens system for imaging consisting, in order from an object side, of a first lens group that has negative refractive power, a second lens group that has positive refractive power, a third lens group that has positive refractive power, a stop, and a fourth lens group that has positive refractive power,
wherein the third lens group includes, at a position closest to an image plane side, a cemented lens disposed on the object side of the stop and including an image plane side-surface with a surface that is concave on the object side,
the fourth lens group includes, at a position closest to the object side, a cemented lens disposed closest to the image plane side of the stop and including an object side surface with a surface that is concave on the image plane side, and a meniscus lens with positive refractive power, being concave on the object side, disposed on the image plane side of the cemented lens disposed on the image plane side of the stop, and
a radius of curvature g 3 er of the surface that is concave on the object side and the radius of curvature g 4 fr of the surface that is concave on the image surface side satisfy a following condition:
2.5≤| g 4 fr/g 3 er|≤ 4.0.

4. The lens system according to claim 3 ,
wherein a radius of curvature B 3 er of a surface, which is convex on the image plane side, on the image plane side of the cemented lens disposed on the image plane side of the stop and a radius of curvature Lbfr of a surface, which is concave on the object side, on the object side of the meniscus lens with positive refractive power satisfy a following condition:
1.35≤| B 3 er/Lbfr|≤ 1.55.

5. The lens system according to claim 3 ,
wherein the fourth lens group includes a cemented lens disposed on the image plane side of the meniscus lens with positive refractive power, and
a radius of curvature Lber of a surface, which is convex on the image plane side, on the image plane side of the meniscus lens with positive refractive power and a radius of curvature B 4 fr of a surface, which is concave on the object side, on the object side of the cemented lens disposed on the image plane side of the meniscus lens with positive refractive power satisfy a following condition:
1.03 ≤|Lber/B 4 fr|≤ 1.07.

6. The lens system according to claim 5 ,
wherein a distance Ld 41 on an optical axis between a surface, which is convex on the image plane side, on the image plane side of the cemented lens disposed on the image plane side of the stop and a surface, which is concave on the object side, on the object side of the meniscus lens with positive refractive power, and a distance Ld 43 on the optical axis between a surface, which is convex on the image plane side, on the image plane side of the meniscus lens with positive refractive power and a surface, which is concave on the object side, on the object side of the cemented lens disposed on the image plane side of the meniscus lens with positive refractive power satisfy a following condition:
7≤ Ld 41/ Ld 43≤23.

7. The lens system according to claim 5 ,
wherein a distance Ld 41 on the optical axis between a surface, which is convex on the image plane side, on the image plane side of the cemented lens disposed on the image plane side of the stop and a surface, which is concave on the object side, on the object side of the meniscus lens with positive refractive power, and a thickness Ld 42 on the optical axis of the meniscus lens with positive refractive power satisfy a following condition:
0.6≤ Ld 41/ Ld 42≤1.0.

8. The lens system according to claim 5 ,
wherein the second lens group includes a first cemented lens and an effective diameter BM of the first cemented lens, an effective diameter B 2 D of a second cemented lens on the object side of the stop in the third lens group, an effective diameter B 3 D of a third cemented lens on the image plane side of the stop in the fourth lens group, and an effective diameter B 4 D of a fourth cemented lens on the image plane side of the lens with positive refractive power in the fourth lens group satisfy following conditions:
B 1 D>B 2 D , and
B 3 D<B 4 D.

9. The lens system according to claim 8 ,
wherein a difference between an Abbe number B 1 p of the lens with positive refractive power and an Abbe number B 1 m of the lens with negative refractive power in the first cemented lens, a difference between an Abbe number B 2 p of the lens with positive refractive power and an Abbe number B 2 m of the lens with negative refractive power in the second cemented lens, a difference between an Abbe number B 3 p of the lens with positive refractive power and an Abbe number B 3 m of the lens with negative refractive power in the third cemented lens, and a difference between an Abbe number B 4 p of the lens with positive refractive power and an Abbe number B 4 m of the lens with negative refractive power in the fourth cemented lens satisfy following conditions:
| B 1 p−B 1 m|<|B 2 p−B 2 m |, and
| B 3 p−B 3 m|>|B 4 p−B 4 m|.

10. An imaging apparatus comprising:
the lens system according to claim 3 ; and
an imaging element disposed on the image plane side of the lens system.

11. A lens system for imaging consisting, in order from an object side, of a first lens group that has negative refractive power, a second lens group that has positive refractive power, a third lens group that has positive refractive power, a stop, and a fourth lens group that has positive refractive power,
wherein the third lens group includes, at a position closest to an image plane side, a cemented lens disposed on the object side of the stop and including an image plane side-surface with a surface that is concave on the object side,
the fourth lens group includes, at a position closest to the object side, a cemented lens disposed closest to the image plane side of the stop and including an object side surface with a surface that is concave on the image plane side, and
during focusing from infinity to a closest distance, a distance between the first lens group and the seco

Assignees

• Nittoh Inc

Inventors

• Miyashita Yuya

Classifications

• G02B15/144515 Primary

  arranged -+++ · CPC title

• G02B13/02

  Telephoto objectives, i.e. systems of the type + - in which the distance from the front vertex to the image plane is less than the equivalent focal length · CPC title

• G02B27/0025

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

• G02B13/26 Primary

  for reproducing with unit magnification · CPC title

• G02B9/64

  having more than six components · CPC title