Rear attachment lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-10838166-B2
Application number	US-201815982962-A
Country	US
Kind code	B2
Filing date	May 17, 2018
Priority date	May 31, 2017
Publication date	Nov 17, 2020
Grant date	Nov 17, 2020

Abstract

The rear attachment lens has a positive refractive power as a whole, and is attached to an image side of a main lens so as to change a focal length of the whole lens system after attachment to a focal length longer than a focal length of the main lens. The rear attachment lens includes a most object side lens that is a lens which has a negative refractive power and is disposed to be closest to an object side, and a most image side lens that is a lens which has a positive refractive power and is disposed to be closest to the image side.

First claim

What is claimed is:

1. A rear attachment lens that is attached to an image side of a main lens as an imaging lens so as to change a focal length of the whole lens system after attachment to a focal length longer than a focal length of the main lens, the rear attachment lens comprising:
a most object side lens that is a lens which has a negative refractive power and is disposed to be closest to an object side; and
a most image side lens that is a lens which has a positive refractive power and is disposed to be closest to the image side,
wherein the rear attachment lens has a positive refractive power as a whole, and
wherein assuming that a partial dispersion ratio of the most object side lens between a g line and an F line is θgL11, and an Abbe number of the most object side lens at a d line is νL11, Conditional Expression (1) below is satisfied:
0.62<θ gL 11+0.001625×ν L 11<0.65  (1).

2. The rear attachment lens according to claim 1 , wherein assuming that a refractive index the most object side lens at the d line is NL11, and an Abbe number of the most object side lens at the d line is νL11, Conditional Expressions (5) and (6) below are satisfied:
1.53< NL 11<1.8  (5)

45<ν L 11<75  (6).

3. The rear attachment lens according to claim 1 , wherein assuming that a focal length of the most object side lens is fL11 and a focal length of the rear attachment lens is fRA, Conditional Expression (7) below is satisfied:
−0.5< fL 11/ fRA<− 0.05  (7).

4. The rear attachment lens according to claim 1 , further comprising:
a three cemented lens that is formed by cementing three lenses consisting of a negative lens, a positive lens, and a negative lens, in order from the object side,
wherein assuming that a partial dispersion ratio of the positive lens in the three cemented lens between the g line and the F line is θgTL2, a partial dispersion ratio of the negative lens closest to the image side in the three cemented lens between the g line and the F line is θgTL3, a refractive index of the positive lens in the three cemented lens at the d line is NTL2, a refractive index of the negative lens closest to the image side in the three cemented lens at the d line is NTL3, and an Abbe number of the positive lens in the three cemented lens at the d line is νTL2, Conditional Expressions (8), (9), and (10) below are satisfied:
−0.03<θ gTL 2−θ gTL 3<0.03  (8)

−0.35< NTL 2− NTL 3<−0.15  (9)

20<ν TL 2<40  (10).

5. The rear attachment lens according to claim 1 , wherein assuming that a distance on an optical axis from a lens surface closest to the object side in the rear attachment lens to an object side principal point of the rear attachment lens is ef, and a distance on the optical axis from the lens surface closest to the object side in the rear attachment lens to a lens surface closest to the image side in the rear attachment lens is RAT, Conditional Expression (11) below is satisfied:
1< ef /RAT<5  (11).

6. The rear attachment lens according to claim 1 , wherein Conditional Expression (1-1) below is satisfied:
0.63<θ gL 11+0.001625×ν L 11<0.64  (1-1).

7. The rear attachment lens according to claim 2 , wherein Conditional Expression (5-1) below is satisfied:
1.55< NL 11<1.76  (5-1).

8. The rear attachment lens according to claim 2 , wherein Conditional Expression (6-1) below is satisfied:
50<ν L 11<70  (6-1).

9. The rear attachment lens according to claim 3 , wherein Conditional Expression (7-1) below is satisfied:
−0.4< fL 11/ fRA<− 0.1  (7-1).

10. The rear attachment lens according to claim 4 , wherein Conditional Expression (9-1) below is satisfied:
−0.3< NTL 2− NTL 3<−0.2  (9-1).

11. The rear attachment lens according to claim 4 , wherein Conditional Expression (10-1) below is satisfied:
28<ν TL 2<37  (10-1).

12. The rear attachment lens according to claim 5 , wherein Conditional Expression (11-1) below is satisfied:
1.5< ef /RAT<4  (11-1).

13. An imaging apparatus comprising:
the main lens; and
the rear attachment lens according to claim 1 .

14. A rear attachment lens that is attached to an image side of a main lens as an imaging lens so as to change a focal length of the whole lens system after attachment to a focal length longer than a focal length of the main lens, the rear attachment lens consisting of, in order from the object side:
a first lens group that has a negative refractive power;
a second lens group that has a positive refractive power; and
a third lens group that has a positive refractive power,
wherein the first lens group consists of, in order from the object side, a most object side lens that is a lens which has a negative refractive power and is disposed to be closest to an object side, and a cemented lens that is formed by cementing at least one negative lens and at least one positive lens,
wherein the second lens group consists of, in order from the object side, a positive lens and a negative lens, and
wherein the third lens group consists of, in order from the object side, a negative lens, a positive lens, a negative lens, and a positive lens.

15. The rear attachment lens according to claim 14 , wherein assuming that a focal length of the first lens group is fG1 and a focal length of the most object side lens is fL11, Conditional Expression (2) below is satisfied:
0.5< fG 1/ fL 11<1.5  (2).

16. The rear attachment lens according to claim 14 ,
wherein a lens closest to the object side in the third lens group and a second lens from the object side in the third lens group are cemented to each other, and
wherein assuming that a partial dispersion ratio of the lens closest to the object side in the third lens group between the g line and the F line is θgL31, a partial dispersion ratio of the second lens from the object side in the third lens group between the g line and the F line is θgL32, a refractive index of the lens closest to the object side in the third lens group at the d line is NL31, and a refractive index of the second lens from the object side in the third lens group at the d line is NL32, Conditional Expressions (3) and (4) below are satisfied:
−0.02<θ gL 31−θ gL 32<0.02  (3)

0.3< NL 31− NL 32<0.5  (4).

17. The rear attachment lens according to claim 15 , wherein Conditional Expression (2-1) below is satisfied:
0.6< fG 1/ fL 11<1.2  (2-1).

18. The rear attachment lens according to claim 16 , wherein Conditional Expression (3-1) below is satisfied:
−0.01<θ gL 31−θ gL 32<0.01  (3-1).

19. The rear attachment lens according to claim 16 , wherein Conditional Expression (4-1) below is satisfied:
0.35< NL 31− NL 32<0.45  (4-1).

20. An imaging apparatus comprising:
the main lens; and
the rear attachment lens according to claim 14 .

Assignees

• Fujifilm Corp

Inventors

• Inukai Hajime

Classifications

• G02B15/12 Primary

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

• G02B15/177 Primary

  having a negative front lens or group of lenses · CPC title

• G02B7/021

  for more than one lens · CPC title

• G02B27/0037

  with diffracting elements (G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876) · CPC title

• G02B9/12 Primary

  having three components only · CPC title