Zoom lens and imaging apparatus

Patent metadata

Field	Value
Publication number	US-11966030-B2
Application number	US-202217580109-A
Country	US
Kind code	B2
Filing date	Jan 20, 2022
Priority date	Jan 21, 2021
Publication date	Apr 23, 2024
Grant date	Apr 23, 2024

Abstract

The zoom lens consists of, in order from an object side to an image side, a first lens group having a negative refractive power, a middle group, and a final group. During zooming, a spacing between the first lens group and the middle group changes, and a spacing between the middle group and the final group changes. During focusing, at least a part of the middle group moves, and the first lens group and the final group remain stationary with respect to an image plane. The zoom lens satisfies predetermined conditional expressions about a back focal length, a focal length, and a maximum half angle of view.

First claim

What is claimed is:

1. A zoom lens consisting of, in order from an object side to an image side, a first lens group that has a negative refractive power, a middle group, and a final group,
wherein during zooming, a spacing between the first lens group and the middle group changes, and a spacing between the middle group and the final group changes,
during focusing, at least a part of the middle group moves along an optical axis as a focus group, and the first lens group and the final group remain stationary with respect to an image plane,
a back focal length of the zoom lens at an air conversion distance at a wide angle end in a state where an infinite distance object is in focus is Bfw,
a focal length of the zoom lens at the wide angle end in the state where the infinite distance object is in focus is fw,
a maximum half angle of view at the wide angle end in the state where the infinite distance object is in focus is ωw,
Conditional Expression (1) is satisfied, which is represented by
0.35<Bfw/(fw×tan|ωw|)<1.5  (1),

an amount of movement of the focus group in a case of changing from the state in which the infinite distance object is in focus to a state in which an imaging magnification is −0.1 times, at a telephoto end, is Dfoct,
a difference in a direction of the optical axis between a position of a lens surface closest to the object side in the middle group at the telephoto end and a position of the lens surface closest to the object side in the middle group at the wide angle end, in the state in which the infinite distance object is in focus, is DpM, and
Conditional Expression (2) is satisfied, which is represented by
0.005<|Dfoct/DpM|<0.3  (2).

2. The zoom lens according to claim 1 , wherein
an effective diameter of a lens surface closest to the object side in the middle group is EDMf,
an effective diameter of a lens surface closest to the image side in the middle group is EDMr, and
Conditional Expression (3) is satisfied, which is represented by
0.3<EDMf/EDMr<1.5  (3).

3. The zoom lens according to claim 1 , wherein a sum of Bfw and a distance on the optical axis from a lens surface closest to the object side in the first lens group at the wide angle end to a lens surface closest to the image side in the final group at the wide angle end is TLw, and Conditional Expression (4) is satisfied, which is represented by
2.5<TLw/(fw×tan|ωw|)<7  (4).

4. The zoom lens according to claim 1 , wherein the middle group includes, in order from the object side to the image side, a front subgroup having a positive refractive power and a rear subgroup having a negative refractive power.

5. The zoom lens according to claim 4 , wherein during focusing, at least a part of the rear subgroup moves along the optical axis, and the other group remains stationary with respect to the image plane.

6. The zoom lens according to claim 4 , wherein during focusing, at least a part of the front subgroup moves along the optical axis, and the other group remains stationary with respect to the image plane.

7. The zoom lens according to claim 4 , wherein the rear subgroup includes an image side negative lens of which an image side surface is a convex surface.

8. The zoom lens according to claim 7 , wherein the rear subgroup includes an object side negative lens of which an object side surface is a convex surface, at a position closer to the object side than the image side negative lens.

9. The zoom lens according to claim 4 , wherein
a paraxial curvature radius of a lens surface closest to the object side in the front subgroup is RMff,
a paraxial curvature radius of a lens surface closest to the image side in the front subgroup is RMfr, and
Conditional Expression (8) is satisfied, which is represented by
−1<(RMff+RMfr)/(RMff−RMfr)<1  (8).

10. The zoom lens according to claim 1 , wherein a distance from the image plane to an exit pupil position at the wide angle end in the state in which the infinite distance object is in focus is Pexpw, and Conditional Expression (9) is satisfied, which is represented by
0.5<Pexpw/fw<5  (9).

11. The zoom lens according to claim 1 , wherein
the first lens group includes a negative meniscus lens of which an object side surface is a convex surface, at a position closest to the object side,
a paraxial curvature radius of the object side surface of the negative meniscus lens is R1f,
a paraxial curvature radius of an image side surface of the negative meniscus lens is R1r, and
Conditional Expression (10) is satisfied, which is represented by
1<(R1f+R1r)/(R1f−R1r)<6  (10).

12. The zoom lens according to claim 1 , wherein the first lens group includes two or more negative meniscus lenses of which object side surfaces are convex surfaces.

13. The zoom lens according to claim 1 , wherein a refractive index of a positive lens included in the first lens group at a d line is N1p, and the first lens group includes one or more positive lenses satisfying Conditional Expression (11), which is represented by
1.6<N1p<2.15  (11).

14. The zoom lens according to claim 1 , wherein a focal length of the first lens group is f1, and Conditional Expression (12) is satisfied, which is represented by
0.3<fw/|f1|<1.5  (12).

15. The zoom lens according to claim 1 , wherein a focal length of the middle group at the wide angle end in the state where the infinite distance object is in focus is fMw, and Conditional Expression (13) is satisfied, which is represented by
0.4<fw/fMw<1.5  (13).

16. The zoom lens according to claim 1 , wherein a focal length of the focus group is ffoc, and Conditional Expression (14) is satisfied, which is represented by
0.05<fw/|ffoc|<2.5  (14).

17. The zoom lens according to claim 1 , wherein an average value of specific gravities of all lenses included in the middle group is GMave, and Conditional Expression (15) is satisfied, which is represented by
3<GMave<4.2  (15).

18. The zoom lens according to claim 1 , wherein a temperature coefficient of a relative refractive index of a negative lens included in the first lens group at a d line in a range of 20° C. to 40° C. is (dN1n/dT)×10 −6 and a unit of dN1n/dT is K −1 , and the first lens group includes one or more negative lenses satisfying Conditional Expression (16), which is represented by
−15<dN1n/dT<0  (16).

19. The zoom lens according to claim 1 , wherein Conditional Expression (1-1) is satisfied, which is represented by
0.45<Bfw/(fw×tan|ωw|)<1.1  (1-1).

20. The zoom lens according to claim 1 , wherein Conditional Expression (1-2) is satisfied, which is represented by
0.5<Bfw/(fw×tan|ωw|)<0.85  (1-2).

21. The zoom lens according to claim 1 , wherein the final group remains stationary with respect to the image plane during zooming.

22. An imaging apparatus comprising the zoom lens according to claim 1 .

23. A zoom lens consisting of, in order from an object side to an image side, a first lens group that has a negative refractive power, a middle group, and a final group,
wherein during zooming, a spacing between the first lens group and the middle group changes, and a spacing between the middle group and the final group changes,
during focusing, at least a part of the middle group moves along an optical axis as a focus group, and the first lens group and the final group remain stationary with respect to an image plane,
a back focal length of the zoom lens at an air conversion distance at a wide angl

Assignees

• Fujifilm Corp

Inventors

• Nagami Ryosuke

Classifications

• G02B15/143507 Primary

  arranged -++ · CPC title

• 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

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

• G02B15/1435 Primary

  the first group being negative · CPC title

• G02B15/144511 Primary

  arranged -+-+ · CPC title