Zoom lens and image pickup apparatus equipped with same

1. A zoom lens in which each of distances between a plurality of lens units changes during zooming from the wide angle end to the telephoto end, comprising:

a focus lens unit that shifts along an optical axis to effect focusing from infinity to a close distance; and

a plurality of wobbling lens units that wobble after a shift of the focus lens unit at an amplitude smaller than the shift of the focus lens unit in focusing operation,

wherein the wobbling lens unit caused to operate is switched in the middle of the zooming from the wide angle end to the telephoto end.

2. An image pickup apparatus comprising a zoom lens according to claim 1 and an image pickup element arranged on the image side of the zoom lens to generate an electrical signal based on an optical image formed by the zoom lens.

3. A zoom lens according to claim 1 , wherein at least one wobbling lens unit among the plurality of wobbling lens units also serves as the focus lens unit that shifts along the optical axis to effect focusing from infinity to a close distance.

4. A zoom lens according to claim 3 , wherein

at the wide angle end, wobbling operation is performed by the first wobbling lens unit A, and the second wobbling lens unit B is stationary while the first wobbling lens unit A is wobbling,

at the telephoto end, wobbling operation is performed by the second wobbling lens unit B, and the first wobbling lens unit A is stationary while the second wobbling lens unit B is wobbling,

the wobbling lens unit caused to wobble is switched over from the first wobbling lens unit A to the second wobbling lens unit B in the middle of zooming from the wide angle end to the telephoto end, and

the zoom lens satisfies the following conditional expression (7):

0.2<( f switch /f w )/( f t /f w )<0.8  (7),

where f switch is the upper limit of the range of focal length of the entire zoom lens system in which wobbling operation is performed using the first wobbling lens unit A, f w is the focal length of the entire zoom lens system at infinity focus at the wide angle end, and f t is the focal length of the entire zoom lens system at infinity focus at the telephoto end.

5. A zoom lens according to claim 1 , wherein a first wobbling lens unit A among the plurality of wobbling lens units wobbles at the wide angle end, a second wobbling lens unit B among the plurality of wobbling lens units wobbles at the telephoto end, and the zoom lens satisfies the following conditional expressions (1) and (2):

|α Aw |/|α Bw |>1  (1), and

|α At |/|α Bt |<1  (2),

where α Aw is the focus sensitivity of the first wobbling lens unit A at infinity focus at the wide angle end, α Bw is the focus sensitivity of the second wobbling lens unit B at infinity focus at the wide angle end, α At is the focus sensitivity of the first wobbling lens unit A at infinity focus at the telephoto end, and α Bt is the focus sensitivity of the second wobbling lens unit B at infinity focus at the telephoto end, the focus sensitivity α of the subject wobbling lens unit at infinity focus at the wide angle end and at the telephoto end being expressed by the following equation:

α=(1−β wob 2 )×β r 2 ,

where β wob is the lateral magnification of the subject wobbling lens unit, and β r is the lateral magnification of the overall optical system on the image side of the subject wobbling lens unit.

6. A zoom lens according to claim 5 , wherein the focus lens unit is a single focus lens unit that shifts along the optical axis to effect focusing from infinity to a close distance at both the wide angle end and the telephoto end.

7. A zoom lens according to claim 5 , wherein the focus lens unit includes a first focus lens unit by which focusing from infinity to a close distance is performed at the wide angle end and a second focus lens unit by which focusing from infinity to a close distance is performed at the telephoto end, the first focus lens unit and the first wobbling lens unit A are the same, and the second focus lens unit and the second wobbling lens unit B are the same.

8. A zoom lens according to claim 5 , wherein the first wobbling lens unit A and the second wobbling lens unit B satisfy the following conditional expression (3):

0≦|α Bw |/|α Aw |<0.6  (3).

9. A zoom lens according to claim 5 , wherein the zoom lens satisfies the following conditional expression (4):

5< M Fw /M Aw   (4),

where M Fw is the maximum shift of the focus lens unit during the focusing operation from infinity to a close distance at the wide angle end, and M Aw is the maximum amplitude of wobbling of the first wobbling lens unit A at the time immediately after the zoom lens is focused at infinity at the wide angle end.

10. A zoom lens according to claim 5 , wherein the zoom lens satisfies the following conditional expression (5):

5< M Ft /M Bt   (4),

where M Ft is the maximum shift of the focus lens unit during the focusing operation from infinity to a close distance at the telephoto end, and M Bt is the maximum amplitude of wobbling of the second wobbling lens unit B at the time immediately after the zoom lens is focused at infinity at the telephoto end.

11. A zoom lens according to claim 5 , wherein the second wobbling lens unit B satisfies the following conditional expression (6):

4<|α Bt |/|α Bw |  (6).

12. A zoom lens according to claim 5 , wherein the first wobbling lens unit A and the second wobbling lens unit B each include three or less lenses.

13. A zoom lens according to claim 12 , wherein the first wobbling lens unit A and the second wobbling lens unit B each include two or less lenses.

14. A zoom lens according to claim 5 , wherein the zoom lens includes a negative lens unit group having a negative refractive power and a positive lens unit group having a positive refractive power, which is arranged on the image side of the negative lens unit group, the negative lens unit group including the second wobbling lens unit B, and the positive lens unit group including the first wobbling lens unit A.

15. A zoom lens according to claim 14 , wherein

the zoom lens includes a first lens unit having a positive refractive power, which is arranged on the object side of the negative lens unit group,

the positive lens unit group includes, in order from the object side, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power, and

during zooming from the wide angle end to the telephoto end, the distance between the first lens unit and the negative lens unit group, the distance between the negative lens unit group and the third lens unit, the distance between the third lens unit and the fourth lens unit, and the distance between the fourth lens unit and the fifth lens unit change.

16. A zoom lens according to claim 15 , wherein

the first lens unit, the third lens unit, and the fifth lens unit are stationary during zooming from the wide angle end to the telephoto end,

the negative lens unit group moves during zooming from the wide angle end to the telephoto end,

the fourth lens unit moves during zooming from the wide angle end to the telephoto end,

the second lens unit serves as the second wobbling lens unit B and a second focus lens unit,

the fourth lens unit serves as the first wobbling lens unit A and a first focus lens unit,

the first focus lens unit is the focus lens unit that performs focusing from infinity to a close distance at the wide angle end, and

the second focus lens unit is the focus lens unit that performs focusing from infinity to a close distance at the telephoto end.

17. A zoom lens according to claim 14 , wherein

the zoom lens includes a first lens unit having a positive refractive power, which is arranged on the object side of the negative lens unit group,

the negative lens unit group includes, in order from the object side, a second lens unit having a negative refractive power and a third lens unit having a negative refractive power,

the positive lens unit group includes, in order from the object side, a fourth lens unit having a positive refractive power and a fifth lens unit having a positive refractive power, and

during zooming from the wide angle end to the telephoto end, the distance between the first lens unit and the second lens unit, the distance between the third lens unit and the fourth lens unit, and the distance between the fourth lens unit and the fifth lens unit change.

18. A zoom lens according to claim 17 , wherein

the fifth lens unit includes, in order from the object side, an object side lens unit and an image side lens unit,

the third lens unit serves as the second wobbling lens unit B and the focus lens unit, and

the object side lens unit in the fifth lens unit serves as the first wobbling lens unit A.

19. A zoom lens according to claim 18 , wherein the distance between the second lens unit and the third lens unit changes during zooming from the wide angle end to the telephoto end.

20. A zoom lens in which each of distances between a plurality of lens units changes during zooming from the wide angle end to the telephoto end, comprising:

a focus lens unit that shifts along an optical axis to effect focusing from infinity to a close distance; and

a plurality of wobbling lens units that wobble after a shift of the focus lens unit at an amplitude smaller than the shift of the focus lens unit in focusing operation.

21. A zoom lens according to claim 20 , wherein the wobbling lens unit caused to operate at the wide angle end and the wobbling lens unit caused to operate at the telephoto end are different from each other.

22. A zoom lens according to claim 20 , wherein the wobbling lens unit caused to operate is switched changes in the middle of the zooming from the wide angle end to the telephoto end.