Variable magnification optical system and imaging apparatus

Patent metadata

Field	Value
Publication number	US-9395522-B2
Application number	US-201313965686-A
Country	US
Kind code	B2
Filing date	Aug 13, 2013
Priority date	Mar 11, 2011
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

A variable magnification optical system consists of a negative first lens group, a stop that is fixed relative to an image plane during magnification change, and a positive second lens group, which are in this order from an object side. A distance between the first lens group and the second lens group in an optical axis direction becomes shorter when magnification is changed from a wide-angle end to a telephoto end. The first lens group consists of a positive lens having a convex object-side surface and two negative lenses, in this order from the object side. The variable magnification optical system satisfies the following formula (1) about Abbe number νd1 of the positive lens in the first lens group for d-line:

25.5<ν d 1<50  (1).

First claim

What is claimed is:

1. A variable magnification optical system consisting of:
a first lens group having negative refractive power;
a stop; and
a second lens group having positive refractive power, which are in this order from an object side,
wherein a distance between the first lens group and the second lens group in an optical axis direction becomes shorter when magnification is changed from a wide-angle end to a telephoto end, and
wherein the stop is fixed relative to an image plane during magnification change, and
wherein the first lens group consists of a positive lens having a convex object-side surface and two negative lenses in this order from the object side, and
wherein the second lens group consists of a double-convex lens, a negative meniscus lens, a double-convex lens, a double-concave lens and a positive lens, which are in this order from the object side,
wherein the following formula (1) is satisfied:
25.5<ν d 1<50  (1), where

νd1: an Abbe number of the positive lens in the first lens group for d-line.

2. The variable magnification optical system, as defined in claim 1 , wherein the following formula (2) is satisfied:
0.8< f 1/ fw< 2.5  (2), where

f1: a focal length of the positive lens in the first lens group, and
fw: a focal length of the optical system at a wide-angle end.

3. The variable magnification optical system, as defined in claim 1 , wherein the following formula (3) is satisfied:
0.5< f 4/ fG 2<1.3  (3), where

f4: a focal length of the double-convex lens on the most object side in the second lens group, and
fG2: a focal length of the second lens group.

4. The variable magnification optical system, as defined in claim 3 , wherein the following formulas (4) through (6) are satisfied:
−0.6< fG 2 F/fG 2 B<− 0.2  (4);

0<ν d 7-ν d 8<25  (5); and

15<ν d 8<33  (6), where

fG2F: a combined focal length of three object-side lenses in the second lens group,
fG2B: a combined focal length of two image-side lenses in the second lens group,
νd7: an Abbe number of the double-concave lens in the second lens group for d-line, and
νd8: an Abbe number of the positive lens in the second lens group for d-line.

5. The variable magnification optical system, as defined in claim 4 , wherein the following formula (6-1) is satisfied:
20<ν d 8<30  (6-1).

6. The variable magnification optical system, as defined in claim 3 , wherein the second lens group includes at least one cemented surface satisfying the following formula (7):
−0.75< Rc/fw< 0.70  (7), where

Rc: a curvature radius of a cemented surface, and
fw: a focal length of the optical system at a wide-angle end.

7. The variable magnification optical system, as defined in claim 3 , wherein the following formula (8) is satisfied:
1.2< H 1/ H 6<1.5  (8), where

H1: a height of a marginal ray of axial rays on a most-object-side surface in the first lens group at a wide-angle end,
H6: a height of a marginal ray of the axial rays on a most-image-side surface in the first lens group at a wide-angle end.

8. The variable magnification optical system, as defined in claim 3 , wherein the following formulas (9) and (10) are satisfied:
1.4< dw/fw< 2.2  (9); and

4.5< Lw/fw< 5.6  (10), where

dw: a distance on an optical axis between the first lens group and the second lens group at a wide-angle end,
fw: a focal length of the optical system at a wide-angle end, and
Lw: an lens length at a wide-angle end.

9. The variable magnification optical system, as defined in claim 1 , wherein the following formulas (4) through (6) are satisfied:
−0.6< fG 2 F/fG 2 B<− 0.2  (4);

0<ν d 7−ν d 8<25  (5); and

15<ν d 8<33  (6), where

fG2F: a combined focal length of three object-side lenses in the second lens group,
fG2B: a combined focal length of two image-side lenses in the second lens group,
νd7: an Abbe number of the double-concave lens in the second lens group for d-line, and
νd8: an Abbe number of the positive lens in the second lens group for d-line.

10. The variable magnification optical system, as defined in claim 9 , wherein the following formula (6-1) is satisfied:
20<ν d 8<30  (6-1).

11. The variable magnification optical system, as defined in claim 1 , wherein the second lens group includes at least one cemented surface satisfying the following formula (7):
−0.75< Rc/fw< 0.70  (7), where

Rc: a curvature radius of a cemented surface, and
fw: a focal length of the optical system at a wide-angle end.

12. The variable magnification optical system, as defined in claim 1 , wherein the following formula (8) is satisfied:
1.2< H 1/ H 6<1.5  (8), where

H1: a height of a marginal ray of axial rays on a most-object-side surface in the first lens group at a wide-angle end,
H6: a height of a marginal ray of the axial rays on a most-image-side surface in the first lens group at a wide-angle end.

13. The variable magnification optical system, as defined in claim 1 , wherein the following formulas (9) and (10) are satisfied:
1.4< dw/fw< 2.2  (9); and

4.5< Lw/fw< 5.6  (10), where

dw: a distance on an optical axis between the first lens group and the second lens group at a wide-angle end,
fw: a focal length of the optical system at a wide-angle end, and
Lw: an lens length at a wide-angle end.

14. The variable magnification optical system, as defined in claim 1 , wherein the following formula (1-1) is satisfied:
29<ν d 1<40  (1-1).

15. The variable magnification optical system, as defined in claim 1 , wherein the following formula (2-1) is satisfied:
1.0< f 1/ fw< 2.0  (2-1), where

f1: a focal length of the positive lens in the first lens group, and
fw: a focal length of the optical system at a wide-angle end.

16. An imaging apparatus comprising:
the variable magnification optical system, as defined in claim 1 ; and
an imaging device that images an optical image formed by the variable magnification optical system, and outputs electrical signals.

Assignees

• Fujifilm Corp

Inventors

• Ono Kazunori

Classifications

• G02B15/177

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

• G02B15/14 Primary

  by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective · CPC title

• G02B15/161

  Physics · mapped topic

• G02B15/1425 Primary

  the first group being negative · CPC title

• G02B15/142

  having two groups only · CPC title