Zoom optical system and imaging apparatus provided with the same

Patent metadata

Field	Value
Publication number	US-9874734-B2
Application number	US-201615240454-A
Country	US
Kind code	B2
Filing date	Aug 18, 2016
Priority date	Sep 8, 2015
Publication date	Jan 23, 2018
Grant date	Jan 23, 2018

Abstract

A zoom optical system includes a negative first lens group having a first deflection optical element, a positive second lens group, a positive third lens group, a positive fourth lens group, and a second deflection optical element, in that order from the object side. The first lens group is provided at a fixed position relative to an imaging plane. Zooming is performed by moving at least the second and third lens groups so that distances between adjacent lens groups of the first through fourth lens groups change. The third lens group is a focusing lens group which moves along the optical axis during focusing. The following condition (1) is satisfied:

0.2< f 3/ f 4<1.0  (1),

wherein f3 designates the focal length of the third lens group, and f4 designates the focal length of the fourth lens group.

First claim

What is claimed is:

1. A zoom optical system comprising a negative first lens group including a first deflection optical element, a positive second lens group, a positive third lens group, a positive fourth lens group, and a second deflection optical element, in that order from the object side,
wherein said first lens group, including said first deflection optical element, is provided at a fixed position relative to an imaging plane,
wherein zooming is performed by moving at least said second lens group and said third lens group along the optical axis so that distances between adjacent lens groups of the first through fourth lens groups change,
wherein said third lens group is a focusing lens group which moves along the optical axis during focusing, and
wherein the following condition (1) is satisfied:
0.2< f 3/ f 4<1.0  (1),

wherein
f3 designates the focal length of said third lens group, and
f4 designates the focal length of said fourth lens group.

2. The zoom optical system according to claim 1 , wherein said second lens group comprises two lens elements including at least one positive lens element, and wherein the following conditions (2) and (3) are satisfied:
4< M 2 t/M 2 w< 10  (2),

and
vd 2 p> 60  (3),

wherein
M2t designates the lateral magnification of said second lens group at the long focal length extremity,
M2w designates the lateral magnification of said second lens group at the short focal length extremity, and
vd2p designates the Abbe number with respect to the d-line of a positive lens element provided closest to the object side within said second lens group.

3. The zoom optical system according to claim 2 , wherein the following condition (3′) is satisfied:
100> vd 2 p> 60  (3′).

4. The zoom optical system according to claim 1 , wherein said second lens group comprises a positive lens element and a negative lens element, wherein the following condition (4) is satisfied:
1<| f 2 n|/f 2<2  (4),

wherein
f2n designates the focal length of the negative lens element provided in said second lens group, and
f2 designates the focal length of said second lens group.

5. The zoom optical system according to claim 1 , wherein the following condition (5) is satisfied:
5< f 3/ fw< 9  (5),

wherein
f3 designates the focal length of said third lens group, and
fw designates the focal length of the entire zoom optical system at the short focal length extremity.

6. The zoom optical system according to claim 1 , wherein said second lens group comprises a positive lens element and a negative lens element, wherein at least one of said positive lens element and said negative lens element includes an aspherical surface.

7. The zoom optical system according to claim 1 , wherein said second lens group comprises two lens elements, and wherein the following condition (6) is satisfied:
−2.2< f 1/ fw<− 1.4  (6),

wherein
f1 designates the focal length of said first lens group, and
fw designates the focal length of the entire zoom optical system at the short focal length extremity.

8. The zoom optical system according to claim 1 , wherein said first lens group comprises at least one negative lens element, and wherein the following condition (7) is satisfied:
0.9< fL 1/ f 1<1.6  (7),

wherein
fL1 designates the focal length of the negative lens element which is provided closest to the object side within said first lens group, and
f1 designates the focal length of said first lens group.

9. The zoom optical system according to claim 1 , wherein said first deflection optical element comprises a first prism, and wherein the following conditions (8) and (9) are satisfied:
0.9< Dp/fw< 1.8  (8),

and
0.9< Dp/Yt< 1.8  (9),

wherein
Dp designates the length of said first prism along the optical axis,
fw designates the focal length of the entire zoom optical system at the short focal length extremity, and
Yt designates the maximum image height at the long focal length extremity.

10. The zoom optical system according to claim 1 , wherein the following condition (10) is satisfied:
0.26< f 2/ f 3<0.47  (10),

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

11. The zoom optical system according to claim 1 , wherein the third lens group comprises a positive lens element and a negative lens element, wherein the following condition (11) is satisfied:
vd 3 p> 70  (11),

wherein
vd3p designates the Abbe number with respect to the d-line of the positive lens element provided within said third lens group.

12. The zoom optical system according to claim 11 , wherein the following condition (11′) is satisfied:
100> vd 3 p> 70  (11′).

13. The zoom optical system according to claim 1 , wherein said fourth lens group is provided at a fixed position relative to an imaging plane, wherein the following condition (12) is satisfied:
6< f 4/ fw< 24  (12),

wherein
f4 designates the focal length of said fourth lens group, and
fw designates the focal length of the entire zoom optical system at the short focal length extremity.

14. The zoom optical system according to claim 1 , wherein said second deflection optical element comprises a second prism.

15. The zoom optical system according to claim 1 , wherein said fourth lens group comprises a positive single lens element.

16. The zoom optical system according to claim 1 , wherein at least one of said first deflection optical element and said second deflection optical element comprises a prism configured to bend an optical path by 90°.

17. A zoom optical system comprising a negative first lens group including a first deflection optical element, a positive second lens group, a positive third lens group, and a positive fourth lens group, in that order from the object side,
wherein said first lens group, including said first deflection optical element, is provided at a fixed position relative to an imaging plane,
wherein zooming is performed by moving at least said second lens group and said third lens group along the optical axis so that distances between adjacent lens groups of the first through fourth lens groups change,
wherein said second lens group includes two lens elements including at least one positive lens element, and wherein the following conditions (2) and (3) are satisfied:
4< M 2 t/M 2 w< 10  (2),

and
vd 2 p> 60  (3),

wherein
M2t designates the lateral magnification of said second lens group at the long focal length extremity,
M2w designates the lateral magnification of said second lens group at the short focal length extremity, and
vd2p designates the Abbe number with respect to the d-line of a positive lens element provided closest to the object side within said second lens group.

18. The zoom optical system according to claim 2 , wherein the following condition (3′) is satisfied:
100> vd 2 p> 60  (3′).

19. A zoom optical system comprising a negative first lens group including a first deflection optical element, a positive second lens group, a positive third lens group, and a positive fourth lens group, in that order from the object side,
wherein said first lens group, including said first deflection optical element, is provided at a fixed position relative to an imaging plane,
wherein zooming is performed by moving at least said second lens group and said third lens group along the optical axis so that distances

Assignees

• Hoya Corp

Inventors

• Takakubo Yutaka
• Tada Eijiroh

Classifications

• G02B13/18

  with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration {(G02B13/002 takes precedence)} · CPC title

• G02B15/177 Primary

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

• G02B9/34

  having four components only · CPC title

• G02B13/009

  having zoom function · CPC title

• G02B15/24

  having a front fixed lens or lens group and two movable lenses or lens groups in front of a fixed lens or lens group · CPC title