Imaging lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-9746653-B2
Application number	US-201514940271-A
Country	US
Kind code	B2
Filing date	Nov 13, 2015
Priority date	Nov 17, 2014
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

An imaging lens is constituted by, in order from the object side to the image side: a first lens group having a negative refractive power; a second lens group having a positive refractive power; a stop; and a third lens group having a positive refractive power or a negative refractive power. The first lens group has at least two positive lenses, a first positive lens from among the at least two positive lenses being positioned most toward the object side, and three negative lenses being consecutively provided adjacent to the first positive lens at the image side thereof. The first lens group is fixed with respect to an imaging surface, and focusing operations are performed by moving the second lens group and the third lens group.

First claim

What is claimed is:

1. An imaging lens consisting of, in order from the object side to the image side:
a first lens group having a negative refractive power;
a second lens group having a positive refractive power;
a stop; and
a third lens group having one of a positive refractive power and a negative refractive power;
the first lens group having at least two positive lenses;
a first positive lens from among the at least two positive lenses being positioned most toward the object side;
three negative lenses being consecutively provided adjacent to the first positive lens at the image side thereof;
the first lens group being fixed with respect to an imaging surface, and focusing operations being performed by moving the second lens group and the third lens group;
a positive lens positioned most toward the image side within the second lens group is designated as a second positive lens; and
Conditional Formula (5) below is satisfied:
−1.7<( R 2 f−R 2 r )/( R 2 f+R 2 r )<−0.8  (5)

wherein R2f is the radius of curvature of the surface toward the object side of the second positive lens, and R2r is the radius of curvature of the surface toward the image side of the second positive lens.

2. An imaging lens as defined in claim 1 , in which Conditional Formula (1) below is satisfied:
−1.2<( R 1 f−R 1 r )/( R 1 f+R 1 r )<0  (1)

wherein R1f is the radius of curvature of the surface toward the object side of the first positive lens, and R1r is the radius of curvature of the surface toward the image side of the first positive lens.

3. An imaging lens as defined in claim 1 , in which Conditional Formula (2) is satisfied:
−2.5< f 1/ f 3<2.5  (2)

wherein f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group.

4. An imaging lens as defined in claim 1 , in which Conditional Formula (3) below is satisfied:
−1.5< f 2/ f 3<1.2  (3)

wherein f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

5. An imaging lens as defined in claim 1 , in which Conditional Formula (4) below is satisfied:
0.1 <f/f 23<0.6  (4)

wherein f is the focal length of the entire lens system, and f23 is the combined focal length of the second lens group and the third lens group.

6. An imaging lens as defined in claim 1 , wherein:
the third lens group to has, in order from the object side to the image side, a first cemented lens formed by cementing a negative meniscus lens having a convex surface toward the object side and a positive lens, provided in this order from the object side to the image side, together, and a second cemented lens formed by cementing a positive lens and a negative meniscus lens having a convex surface toward the image side, provided in this order from the object side to the image side, together; and
Conditional Formula (6) below is satisfied:
40<ν p 3−ν n 3≦56.740  (6)

wherein νp3 is the Abbe's number of the positive lens of the second cemented lens with respect to the d line, and νn3 is the Abbe's number of the negative meniscus lens of the second cemented lens with respect to the d line.

7. An imaging lens as defined in claim 1 , in which Conditional Formulae (7) and (8) below are satisfied:
1.806≦−0.005 νd 1+2.01≦ nd 1  (7)

ν d 1<53  (8)

wherein νd1 is the Abbe's number of the first positive lens with respect to the d line, and nd1 is the refractive index of the first positive lens with respect to the d line.

8. An imaging lens as defined in claim 1 , wherein:
the second lens group and the third lens group approach each other when changing focus from an object at infinity to an object at a close distance.

9. An imaging lens as defined in claim 1 , in which Conditional Formula (1-1) below is satisfied:
−0.8<( R 1 f−R 1 r )/( R 1 f+R 1 r )<−0.1  (1-1)

wherein R1f is the radius of curvature of the surface toward the object side of the first positive lens, and R1r is the radius of curvature of the surface toward the image side of the first positive lens.

10. An imaging lens as defined in claim 1 , in which Conditional Formula (2-1) below is satisfied:
−1.5< f 1/ f 3<1.5  (2-1)

wherein f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group.

11. An imaging lens as defined in claim 1 , in which Conditional Formula (3-1) below is satisfied:
−1.2< f 2/ f 3<1  (3-1)

wherein f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

12. An imaging lens as defined in claim 1 , in which Conditional Formula (4-1) below is satisfied:
0.2< f/f 23<0.5  (4-1)

wherein f is the focal length of the entire lens system, and f23 is the combined focal length of the second lens group and the third lens group.

13. An imaging lens as defined in claim 1 , wherein:
the third lens group to has, in order from the object side to the image side, a first cemented lens formed by cementing a negative meniscus lens having a convex surface toward the object side and a positive lens, provided in this order from the object side to the image side, together, and a second cemented lens formed by cementing a positive lens and a negative meniscus lens having a convex surface toward the image side, provided in this order from the object side to the image side, together; and Conditional Formula (6-1) below is satisfied:
50<ν p 3−ν n 3≦56.740  (6-1)

wherein νp3 is the Abbe's number of the positive lens of the second cemented lens with respect to the d line, and νn3 is the Abbe's number of the negative meniscus lens of the second cemented lens with respect to the d line.

14. An imaging lens as defined in claim 1 , in which Conditional Formulae (7-1) and (8) below are satisfied:
1.806≦−0.0059 νd 1+2.061≦ nd 1  (7-1)

ν d 1<53  (8)

wherein νd1 is the Abbe's number of the first positive lens with respect to the d line, and nd1 is the refractive index of the first positive lens with respect to the d line.

15. An imaging apparatus equipped with an imaging lens as defined in claim 1 .

Assignees

• Fujifilm Corp

Inventors

• Sun Ping

Classifications

• G02B15/22 Primary

  with movable lens means specially adapted for focusing at close distances · CPC title

• G02B15/177 Primary

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

• G02B13/04

  Reversed telephoto objectives · CPC title