Rear converter lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-11079573-B2
Application number	US-201916453653-A
Country	US
Kind code	B2
Filing date	Jun 26, 2019
Priority date	Jul 13, 2018
Publication date	Aug 3, 2021
Grant date	Aug 3, 2021

Abstract

A rear converter lens consists of, in order from the object side, a positive first lens group, a negative second lens group, and a positive third lens group. 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, and the third lens group consists of, in order from the object side, a third lens group-first lens that is a positive lens convex toward the object side and a third lens group-second lens that is a negative lens.

First claim

What is claimed is:

1. A rear converter lens having a negative refractive power and being mounted on an image side of a master lens to thereby make a focal length of a whole system including the master lens larger than a focal length of the master lens alone, the rear converter lens consisting of, in order from an object side:
a first lens group having a positive refractive power;
a second lens group having a negative refractive power; and
a third lens group having a positive refractive power,
wherein the first lens group consists of a cemented lens in which, in order from the object side, 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, in order from the object side, a negative lens concave toward the image side, a biconvex positive lens, and a negative lens concave toward the object side are cemented,
the third lens group consists of, in order from the object side, a third lens group-first lens that is a positive lens convex toward the object side and a third lens group-second lens that is a negative lens,
assuming that a focal length of the first lens group is f1, a focal length of the second lens group is f2, a focal length of the third lens group is f3, a focal length of the whole rear converter lens is fC, 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 Expressions (1), (2), (3) and (4) are satisfied:
−1.4< f 1/ fC<− 0.8  (1)

0.2< f 2/ fC< 0.5  (2)

−2.5< f 3/ fC<− 0.7  (3)

0<ν1−ν2<10  (4)

assuming that a focal length of the third lens group-first lens is f31 and a focal length of the third lens group-second lens is f32, Conditional Expressions (5) and (6) are satisfied:
0.3< f 31/ f 3<0.8  (5),

−2.5< f 32/ f 3<−0.6  (6), and

at least one of lens surfaces of the third lens group-first lens is aspherical.

2. The rear converter lens according to claim 1 ,
wherein Conditional Expression (1-1) is further satisfied:
−1.3< f 1/ fC<− 0.9  (1-1).

3. The rear converter lens according to claim 1 ,
wherein Conditional Expression (2-1) is further satisfied:
0.25< f 2/ fC< 0.4  (2-1).

4. The rear converter lens according to claim 1 ,
wherein Conditional Expression (3-1) is satisfied:
−2.2< f 3/ fC<− 0.8  (3-1).

5. The rear converter lens according to claim 1 ,
wherein Conditional Expression (4-1) is further satisfied:
3<ν1−ν2<8  (4-1).

6. The rear converter lens according to claim 1 ,
wherein Conditional Expression (5-1) is further satisfied:
0.4< f 31/ f 3<0.7  (5-1).

7. The rear converter lens according to claim 1 ,
wherein Conditional Expression (6-1) is further satisfied:
−2.2< f 32/ f 3<−0.7  (6-1).

8. An imaging apparatus comprising the rear converter lens according to claim 1 .

Assignees

• Fujifilm Corp

Inventors

• Ori Tetsuya

Classifications

• G02B9/14

  arranged + - + · 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

• G02B9/64

  having more than six components · CPC title

• G02B9/22

  the middle component having the compound · CPC title

• G02B9/24

  two of the components having compound lenses (G02B9/30 takes precedence) · CPC title