Zoom lens system

1. A zoom lens system comprises a negative first lens group, a diaphragm, and a positive second lens group, in this order from an object,

wherein zooming is performed by moving said negative first lens group and said positive second lens group along an optical axis of said zoom lens system;

wherein said negative first lens group comprises a negative first lens element, a negative second lens element, and a positive third lens element, in this order from the object; and

wherein said zoom lens system satisfies the following conditions:

0.7 < ft/f 2 G < 1.1

3.0 <( d 12 w−d 12 t )/( ft/fw )<5.0

wherein

ft designates the focal length of the entire zoom lens system at the long focal length extremity;

f2G designates the focal length of said positive second lens group; d12w designates the distance between said negative first lens group and said positive second lens group at the short focal length extremity;

d12w designates the distance between said negative first lens group and said positive second lens group at the short focal length extremity;

d12t designates the distance between said negative first lens group and said positive second lens group at the lone focal length extremity: and

fw designates the focal length of the entire zoom lens system at the short focal length extremity.

2. The zoom lens system according to claim 1 , further satisfying the following condition:

3.0 <Σ2 G /( ft/fw )<4.0

wherein

Σ20 G designates the thickness of aid positive second lens group, i.e., the distance from the most object-side surface of said positive second lens group to the most image-side surface thereof; and

fw designates the focal length of the entire zoom lens system at the short focal length extremity.

3. The zoom lens system according to claim 1 , further satisfying of the following condition:

0.6< f 1 n/f 2 n <1.2

wherein

f1n designates the focal length of said negative first lens element of said negative first lens group; and

f2n designates the focal length of said negative second lens element of said negative first lens group.

4. The zoom lens system according to claim 1 , wherein said negative second lens element of said negative first lens group comprises a negative biconcave lens element.

5. The zoom lens system according to claim 1 , wherein said positive second lens group comprises a positive first lens element, a positive second lens element, a negative third lens element, and a positive fourth lens element, in this order from the object.

6. The zoom lens system according to claim 5 , satisfying the following condition:

νp−νn> 23

wherein

νp designates the Abbe number of said positive second lens element of said positive second lens group; and

νn designates the Abbe number of said negative third lens element of said positive second lens group.

7. The zoom lens system according to claim 5 , wherein said positive fourth lens element of said positive second lens group comprises at least one aspherical surface.

8. The zoom lens system according to claim 1 , farther satisfying the following condition:

−1.1< ft/f 1 G<− 0.6

wherein

f1G designates the focal length of said negative first lens group.

9. The zoom lens system according to claim 1 , wherein said diaphragm is stationary at a predetermined position along the optical axis so that the distance between said diaphragm and the image plane of said zoom lens system does not vary.

10. A zoom lens system comprising: a negative first lens group; a diaphragm; and a positive second lens group, in this order from an object, wherein:

zooming is performed by moving said negative first lens group and said positive second lens group along an optical axis of said zoom lens system;

said negative first lens group comprises a negative first lens element, a negative second lens element, and a positive third lens element, in this order from the object; and

said zoom lens system satisfies the following conditions:

0.7< ft/f 2 G< 1.1

3.0<Σ2 G/ ( ft/fw )<4.0

wherein

ft designates the focal length of the entire zoom lens system at the long focal length extremity;

f2G designates the focal length of said positive second lens group;

Σ2G designates the thickness of said positive second lens group, i.e., the distance from the most object-side surface of said positive second lens group to the most image-side surface thereof; and

fw designates the focal length of the entire zoom lens system at the short focal length extremity.

11. The zoom lens system according to claim 10 , further satisfying of the following condition:

0.6< f 1 n/f 2 n< 1.2

wherein

f1n designates the focal length of said negative first lens element of said negative first lens group; and

f2n designates the focal length of said negative second lens element of said negative first lens group.

12. The zoom lens system according to claim 10 , wherein said negative second lens element of said negative first lens group comprises a negative biconcave lens element.

13. The zoom lens system according to claim 10 , wherein said positive second lens group comprises a positive first lens element, a positive second lens element, a negative third lens element, and a positive fourth lens element, in this order from the object.

14. The zoom lens system according to claim 13 , wherein said positive fourth lens element of said positive second lens group comprises at least one aspherical surface.

15. The zoom lens system according to claim 13 , satisfying the following condition:

ν p−νn> 23

wherein

νp designates the Abbe number of said positive second lens element of said positive second lens group; and

νn designates the Abbe number of said negative third lens element of said positive second lens group.

16. The zoom lens system according to claim 10 , further satisfying the following condition:

−1.1< ft/f 1 G<− 0.6

wherein

f1G designates the focal length of said negative first lens group.

17. The zoom lens system according to claim 10 , wherein said diaphragm is stationary at a predetermined position along the optical axis so that the distance between said diaphragm and the image plane of said zoom lens system does not vary.

18. A zoom lens system comprising a negative first lens group; a diaphragm; and a positive second lens group, in this order from an object, wherein:

zooming is performed by moving said negative first lens group and said positive second lens group along an optical axis of said zoom lens system;

said negative first lens group comprises a negative first lens element, a negative second lens element, and a positive third lens element, in this order from the object; and

said zoom lens system satisfies the following conditions:

0.7< ft/f 2 G< 1.1

0.6< f 1 n/f 2 n< 1.2

wherein

ft designates the focal length of the entire zoom lens system at the long focal length extremity;

f2G designates the focal length of said positive second lens group,

f1n designates the focal length of said negative first lens element of said negative first lens group; and

f2n designates the focal length of said negative second lens element of said negative first lens group.

19. The zoom lens system according to claim 18 , wherein said negative second lens element of said negative first lens group comprises a negative biconcave lens element.

20. The zoom lens system according to claim 18 , wherein said positive second lens group comprises a positive first lens element, a positive second lens element, a negative third lens clement, and a positive fourth lens element, in this order from the object.

21. The zoom lens system according to claim 20 , satisfying the following condition:

ν p−νn> 23

wherein

νp designates the Abbe number of said positive second lens element of said positive second lens group; and

νn designates the Abbe number of said negative third lens element of said positive second lens group.

22. The zoom lens system according to claim 20 , wherein said positive fourth lens element of said positive second lens group comprises at least one aspherical surface.

23. The zoom lens system according to claim 18 , further satisfying the following condition:

−1.1< ft/f 1 G<− 0.6

wherein

f1G designates the focal length of said negative first lens group.

24. The zoom lens system according to claim 18 , wherein said diaphragm is stationary at a predetermined position along the optical axis so that the distance between said diaphragm and the image plane of said zoom lens system does not vary.

25. A zoom lens system comprising: a negative first lens group; a diaphragm; and a positive second lens group, in this order from an object, wherein:

said positive second lens group consists of a positive first lens element, a positive second lens element, a negative third lens element, and a positive fourth lens element, in this order from the object;

said positive fourth lens element of said positive second lens group comprises at least one aspherical surface,

zooming is performed by moving said negative first lens group and said positive second lens group along an optical axis of said zoom lens system;

said negative first lens group comprises a negative first lens element, a negative second lens element, and a positive third lens element, in this order from the object; and

said zoom lens system satisfies the following condition:

0.7< fi/f 2 G< 1.1

wherein

ft designates the focal length of the entire zoom lens system at the long focal length extremity; and

f2G designates the focal length of said positive second lens group.

26. The zoom lens system according to claim 25 , wherein said negative second lens element of said negative first lens group comprises a negative biconcave lens element.

27. The zoom lens system according to claim 25 , satisfying the following condition:

ν p−νn> 23

wherein

νp designates the Abbe number of said positive second lens element of said positive second lens group; and

νn designates the Abbe number of said negative third lens element of said positive second lens group.

28. The zoom lens system according to claim 25 , further satisfying the following condition:

−1.1< ft/f 1 G<− 0.6

wherein

f1G designates the focal length of said negative first lens group.

29. The zoom lens system according to claim 25 , wherein said diaphragm is stationary at a predetermined position along the optical axis so that the distance between said diaphragm and the image plane of said zoom lens system does not vary.