Zoom lens, and imaging apparatus incorporating the same

1. A zoom lens, which comprises, in order from an object side thereof:

a first lens group of negative refracting power,

a second lens group of positive refracting power,

a third lens group of negative refracting power, and

a fourth lens group of positive refracting power,

wherein:

upon zooming from a wide-angle end to a telephoto end of the zoom lens,

a separation between the respective lens groups changes,

upon focusing from a focusing-on-infinity state to a close-range focusing state, the third lens group moves in an optical axis direction, and

the following conditions (1) and (2) are satisfied at the wide-angle end:

|(100*( y 1′ −y 1)/ y 1)|/Δ s< 1.2  (1)

|(100*( y 0.7′ −y 0.7)/ y 0.7)|/Δ s< 1.2  (2)

where y1 is a maximum image height on an imaging plane,

y0.7 is seven-tenth of the maximum image height,

y1′ is a ray height at a position where, when there is a defocus quantity of Δs from time of focusing on infinity as the fourth lens group is moved to an object at infinity, a chief ray having the same angle of view as an image-taking angle of view reaching the image height y1 upon focusing on infinity intersects the imaging plane,

y0.7′ is a ray height at a position where, when there is a defocus quantity of Δs from time of focusing on infinity as the fourth lens group is moved to an object at infinity, a chief ray having the same angle of view as an image-taking angle of view reaching the image height y0.7 upon focusing on infinity intersects the imaging plane, and

Δs is 8*the maximum image height y1/1000, provided that y1, y0.7, y1′, y0.7′ and Δs are all given in mm.

2. The zoom lens according to claim 1 , wherein:

a total number of lens groups in the zoom lens is 4.

3. The zoom lens according to claim 1 , wherein:

the third lens group wobbles in the optical axis direction prior to focusing.

4. The zoom lens according to claim 1 , which satisfies the following Conditions (1-1)′ and (2-1)′:

|(100*( y 1′ −y 1)/ y 1)|/Δ s< 0.7  (1-1)′

|(100*( y 0.7′ −y 0.7)/ y 0.7)|/Δ s< 0.7  (2-1)′.

5. The zoom lens according to claim 1 , wherein:

upon zooming, the first lens group remains fixed in position.

6. The zoom lens according to claim 1 , wherein:

the third lens group consists of two lenses at most, with one of the two lenses being a negative lens.

7. The zoom lens according to claim 6 , wherein:

the third lens group consists of a negative lens.

8. The zoom lens according to claim 6 , wherein:

the third lens group consists of:

a positive lens, and

a negative lens.

9. The zoom lens according to claim 8 , wherein:

the positive lens and the negative lens are cemented together.

10. The zoom lens according to claim 1 , which satisfies the following Condition (14):

0.8 <fbw/fw< 1.8  (14)

where fbw is a distance, as calculated on an air basis, from an image-side surface of a lens on the most image side of the zoom lens to an imaging plane upon focusing on infinity at the wide-angle end, and

fw is a focal length of the whole zoom lens system upon focusing on infinity at the wide-angle end.

11. The zoom lens according to claim 1 , which satisfies the following Conditions (5)′, (6)′, (7)′ and (8)′:

−2.5 <f 1 /fw<− 0.5  (5)′

0.5 <f 2 /fw< 2.5  (6)′

−5.0 <f 3 /fw<− 1.0  (7)′

2.0 <f 4 /fw< 10.0  (8)′

where fw is a focal length of the whole zoom lens system upon focusing on infinity at the wide-angle end,

f1 is a focal length of the first lens group,

f2 is a focal length of the second lens group,

f3 is a focal length of the third lens group, and

f4 is a focal length of the fourth lens group.

12. The zoom lens according to claim 1 , wherein:

the second lens group comprises a plurality of lenses, and

there is an aperture stop located on an object side with respect to a position where an air separation between lenses in the second lens group becomes the widest.

13. The zoom lens according to claim 12 , wherein:

upon zooming, the aperture stop moves in unison with the second lens group.

14. The zoom lens according to claim 12 , which satisfies the following Condition (15):

0.08 <d 2 m/dG 2<0.5  (15)

where d2m is a maximum value of an air separation distance between lenses in the second lens group, and

dG2 is an axial thickness of the second lens group from an object-side refracting surface to an image-side refracting surface.

15. The zoom lens according to claim 1 , which satisfies the following Condition (11):

8.0 <y 1<25.0  (11)

where y1 is a maximum image height at the imaging plane throughout the zoom lens system.

16. The zoom lens according to claim 1 , wherein:

upon zooming, the fourth lens group remains fixed in position.

17. The zoom lens according to claim 16 , wherein:

upon focusing from a focusing-on-infinity state to a close-range focusing state, the third lens group moves to the image side, and

upon zooming from the wide-angle end to the telephoto end, the second lens group, and the third lens group moves to the object side.

18. The zoom lens according to claim 1 , which satisfies the following Conditions (12)′ and (13)′:

2.5 <ft/fw< 7.0  (12)′

35 °<ωw< 50°  (13)′

where fw is a focal length of the whole zoom lens system upon focusing on infinity at the wide-angle end,

ft is a focal length of the whole zoom lens system upon focusing on infinity at the telephoto end, and

ωw is a maximum half angle of view of the whole zoom lens system upon focusing on infinity at the wide-angle end.

19. An imaging apparatus, comprising:

a zoom lens as recited in claim 1 , and

an imaging device.