Rear converter lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-11029488-B2
Application number	US-202017020521-A
Country	US
Kind code	B2
Filing date	Sep 14, 2020
Priority date	Sep 15, 2017
Publication date	Jun 8, 2021
Grant date	Jun 8, 2021

Abstract

The rear converter lens consists of, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a negative refractive power; and a third lens group that has a positive refractive power. The first lens group consists of a cemented lens in which a negative lens concave toward the image side and a positive lens convex toward the object side are cemented. The second lens group consists of a cemented lens in which a negative lens concave toward the image side, a positive lens convex toward both sides, and a negative lens concave toward the object side are cemented. The third lens group consists of a cemented lens in which a positive lens convex toward the object side and a negative lens are cemented. The rear converter lens satisfies predetermined Conditional Expressions (1) and (2).

First claim

What is claimed is:

1. An optical system that has a negative refractive power and is mounted on an image side of a master lens so as to make a focal length of a whole system including the master lens larger than a focal length of the master lens alone, the optical system consisting of, in order from an object side:
a first lens group that has a positive refractive power;
a second lens group that has a negative refractive power; and
a third lens group that has a positive refractive power,
wherein the first lens group consists of a negative lens concave toward the image side and a positive lens convex toward the object side in order from the object side,
wherein the second lens group consists of a cemented lens in which a negative lens concave toward the image side, a positive lens convex toward both sides, and a negative lens concave toward the object side are cemented in order from the object side,
wherein the third lens group includes, closest to the object side, a cemented lens in which a positive lens convex toward the object side and a negative lens are cemented in order from the object side, a lens surface closest to an image side of the third lens group has a convex shape toward the image side.

2. The optical system according to claim 1 ,
wherein the negative lens of the first lens group has a meniscus shape concave toward the image side.

3. The optical system according to claim 1 ,
wherein the positive lens of the first lens group has a shape convex toward both sides.

4. The optical system according to claim 1 ,
wherein the negative lens closest to the object side of the second lens group has a shape concave toward both sides.

5. The optical system according to claim 1 ,
wherein the positive lens of the third lens group has a shape convex toward both sides.

6. The optical system according to claim 1 ,
wherein the negative lens of the third lens group has a shape concave toward both sides.

7. An imaging apparatus comprising the optical system according to claim 1 .

8. The optical system according to claim 1 ,
wherein assuming that
a focal length of the first lens group is f1, and
a focal length of the optical system is fC,
Conditional Expression (1) is satisfied,
−1.4< f 1/ fC<− 0.5  (1).

9. The optical system according to claim 8 ,
wherein Conditional Expression (1-1) is satisfied,
−1.35< f 1/ fC<− 0.7  (1-1).

10. The optical system according to claim 1 ,
wherein assuming that
a focal length of the second lens group is f2, and
a focal length of the optical system is fC,
Conditional Expression (2) is satisfied,
0.2< f 2/ fC< 0.36  (2).

11. The optical system according to claim 10 ,
wherein Conditional Expression (2-1) is satisfied,
0.25< f 2/ fC< 0.35  (2-1).

12. The optical system according to claim 1 ,
wherein assuming that
a focal length of the third lens group is f3, and
a focal length of the optical system is fC,
Conditional Expression (3) is satisfied,
−1.5< f 3/ fC<− 0.8  (3).

13. The optical system according to claim 12 ,
wherein Conditional Expression (3-1) is satisfied,
−1.3< f 3/ fC<− 0.9  (3-1).

14. The optical system according to claim 1 ,
wherein assuming that
an Abbe number of the negative lens of the first lens group is ν1, and
an Abbe number of the positive lens of the first lens group is ν2,
Conditional Expression (4) is satisfied,
12<ν1−ν2<45  (4).

15. The optical system according to claim 14 ,
wherein Conditional Expression (4-1) is satisfied,
14<ν1−ν2<40  (4-1).

Assignees

• Fujifilm Corp

Inventors

• Ori Tetsuya

Classifications

• G02B15/12 Primary

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

• G02B9/30 Primary

  the middle component being a - compound meniscus having a + lens · CPC title