Imaging lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-10061102-B2
Application number	US-201615272592-A
Country	US
Kind code	B2
Filing date	Sep 22, 2016
Priority date	Sep 28, 2015
Publication date	Aug 28, 2018
Grant date	Aug 28, 2018

Abstract

An imaging lens consists of, in order from the object side, a first lens group fixed during focusing, and a positive second lens group moved toward the object side during focusing from a distant object to a close object. The second lens group consists of, in order from the object side, a first cemented lens consisting of a biconvex lens and a negative lens having a smaller absolute value of curvature radius of the object-side surface than that of the image-side surface, and a second cemented lens as a whole having a positive refractive power and consisting of a negative lens having a smaller absolute value of curvature radius of the image-side surface than that of the object-side surface and a positive lens having a smaller absolute value of curvature radius of the object-side surface than that of the image-side surface. The imaging lens satisfies specific condition expressions.

First claim

What is claimed is:

1. An imaging lens consisting of, in order from the object side, a first lens group that is fixed relative to an image plane during focusing, and a second lens group that is moved as a whole from the image side toward the object side during focusing from a distant object to a close object and as a whole has a positive refractive power, wherein:
the second lens group consists of, in order from the object side,
a first cemented lens consisting of, in order from the object side, a biconvex lens and a negative lens having a smaller absolute value of radius of curvature of the object-side surface than that of the image-side surface, and
a second cemented lens as a whole having a positive refractive power and consisting of, in order from the object side, a negative lens having a smaller absolute value of radius of curvature of the image-side surface than that of the object-side surface and a positive lens having a smaller absolute value of radius of curvature of the object-side surface than that of the image-side surface,
a stop that is fixed relative to the image plane during focusing is disposed at a position between the most object-side lens surface of the first lens group and the most object-side lens surface of the second lens group, and
all the condition expressions (1) to (5) below are satisfied:
N21<N22  (1),

ν22<ν21  (2),

N24<N23  (3),

ν23<ν24  (4), and

0.2< D/f< 0.8  (5),

where N21 is a refractive index with respect to the d-line of the biconvex lens of the first cemented lens, N22 is a refractive index with respect to the d-line of the negative lens of the first cemented lens, N23 is a refractive index with respect to the d-line of the negative lens of the second cemented lens, N24 is a refractive index with respect to the d-line of the positive lens of the second cemented lens, ν21 is an Abbe number with respect to the d-line of the biconvex lens of the first cemented lens, ν22 is an Abbe number with respect to the d-line of the negative lens of the first cemented lens, ν23 is an Abbe number with respect to the d-line of the negative lens of the second cemented lens, ν24 is an Abbe number with respect to the d-line of the positive lens of the second cemented lens, D is an equivalent air distance along the optical axis between the first cemented lens and the second cemented lens, and f is a focal length of the entire system when the imaging lens is focused on an object at infinity.

2. The imaging lens as claimed in claim 1 , wherein the first cemented lens as a whole has a positive refractive power.

3. The imaging lens as claimed in claim 1 , wherein the first lens group as a whole has a positive refractive power.

4. The imaging lens as claimed in claim 1 , wherein the condition expression (6) below is satisfied:
0< f/f 1<0.6  (6),

where f1 is a focal length of the first lens group.

5. The imaging lens as claimed in claim 4 , wherein the condition expression (6-1) below is satisfied:
0.1< f/f 1<0.5  (6-1),

6. The imaging lens as claimed in claim 1 , wherein the condition expression (7) below is satisfied:
0.3< f/f 2<0.8  (7),

where f2 is a focal length of the second lens group.

7. The imaging lens as claimed in claim 6 , wherein the condition expression (7-1) below is satisfied:
0.4< f/f 2<0.7  (7-1).

8. The imaging lens as claimed in claim 1 , wherein the condition expression (8) below is satisfied:
0<β2<0.6  (8),

where β2 is a lateral magnification of the second lens group when the imaging lens is focused on an object at infinity.

9. The imaging lens as claimed in claim 8 , wherein the condition expression (8-1) below is satisfied:
0.1<β2<0.5  (8-1).

10. The imaging lens as claimed in claim 1 , wherein the condition expression (9) below is satisfied:
0.25< N 22− N 21<0.6  (9).

11. The imaging lens as claimed in claim 1 , wherein the condition expression (10) below is satisfied:
25<ν21−ν22<70  (10).

12. The imaging lens as claimed in claim 1 , wherein the condition expression (11) below is satisfied:
0.25< N 23− N 24<0.7  (11).

13. The imaging lens as claimed in claim 1 , wherein the condition expression (12) below is satisfied:
40<ν24−ν23<75  (12).

14. The imaging lens as claimed in claim 1 , wherein the first lens group includes, successively in order from the most object side, a single lens having a positive refractive power and a single lens having a negative refractive power.

15. The imaging lens as claimed in claim 1 , wherein the first lens group includes, successively in order from the most image side, a positive lens, a positive lens, and a negative lens.

16. The imaging lens as claimed in claim 1 , wherein the most image-side lens of the first lens group has a convex surface toward the image side.

17. The imaging lens as claimed in claim 1 , wherein the first lens group consists of at least five and not more than seven lenses.

18. The imaging lens as claimed in claim 1 , wherein the condition expression (5-1) below is satisfied:
0.25< D/f <0.7  (5-1).

19. An imaging apparatus comprising the imaging lens as claimed in claim 1 .

Assignees

• Fujifilm Corp

Inventors

• Naruse Yousuke
• Cho Michio

Classifications

• G02B13/04 Primary

  Reversed telephoto objectives · CPC title

• G02B13/22

  Telecentric objectives or lens systems · CPC title

• G02B9/64 Primary

  having more than six components · CPC title

• G02B27/0025

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

• G02B15/163 Primary

  having a first movable lens or lens group and a second movable lens or lens group, both in front of a fixed lens or lens group (G02B15/177 takes precedence) · CPC title