Wide-angle zoom lens system

1. A wide-angle zoom lens system comprising a negativefirst lens group, a positive second lens group, a negative third lens group and a positivefourth lens group, in this order from an object;

wherein upon zooming from the short focal length extremity to the long focallength extremity, a distance between said negative first lens group and said positive second lens group decreases, a distance between said positive second lens group and saidnegative third lens group increases, and a distance between said negative third lens group and said positive fourth lens group decreases; and

wherein said wide-angle zoom lens system satisfies the following conditions:

1.6< X 2/ fw< 3.5

1.2<| f 1|/ fw< 2.0 ( f 1<0)

1.6< f 2/ fw< 2.7

0.9 <X 2 /f 2<1.6

wherein

X 2 designates the traveling distance of said positive second lens group uponzooming from the short focal length extremity to the long focal length extremity;

f 1 designates the focal length of said negative first lens group;

f 2 designates the focal length of said positive second lens group; and

fw designates the focal length of the entire wide-angle zoom lens system at theshort focal length extremity.

2. The wide-angle zoom lens system according to claim 1 , furthersatisfying the following conditions:

2.0< fBw×fBw /( f 1× f 3)<6.0

1.2< f 2/| f 1|<1.8

1.0< f 4/| f 3|<1.8

wherein

fBw designates the equivalent air thickness from the most image-side lenssurface to the image plane at the short focal length extremity;

f 1 designates the focal length of said negative first lens group;

f 2 designates the focal length of said positive second lens group;

f 3 designates the focal length of said negative third lens group; and

f 4 designates the focal length of said positive fourth lens group.

3. The wide-angle zoom lens system according to claim 1 , whereinsaid negative first lens group comprises a negative meniscus lens element having theconvex surface facing toward the object, another negative meniscus lens element havingthe convex surface facing toward the object, a negative lens element having a concavesurface facing toward an image and a positive lens element, in this order from the object.

4. The wide-angle zoom lens system according to claim 1 , whereinsaid negative first lens group comprises a positive lens element, a negative meniscus lenselement having the convex surface facing toward the object, another negative meniscuslens element having the convex surface facing toward the object, a negative lens elementhaving a concave surface facing toward an image and a positive lens element, in thisorder from the object.

5. The wide-angle zoom lens system according to claim 1 , whereinsaid positive second lens group comprises positive cemented lens elements and a positivelens element.

6. The wide-angle zoom lens system according to claim 1 , whereinsaid negative third lens group comprises negative cemented lens elements and a positivelens element, or, two sets of negative cemented lens elements.

7. The wide-angle zoom lens system according to claim 1 , whereinsaid positive fourth lens group comprises cemented lens elements and two positive lenselements.

8. A wide-angle zoom lens system comprising a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from an object:

wherein upon zooming from the short focal length extremity to the long focal length extremity, a distance between said negative first lens group and said positive second lens group decreases, a distance between said positive second lens group and said negative third lens group increases, and a distance between said negative third lens group and said positive fourth lens group decreases; and

wherein said wide-angle zoom lens system satisfies the following conditions:

1.6< X 2/ fw< 3.5

1.2<| f 1|/ fw< 2.0 ( f 1<0)

1.6< f 2/ fw< 2.7

0.5< f 1/ f 3<0.9

0.6< f 2/ f 4<0.9

wherein

X 2 designates the traveling distance of said positive second lens group upon zooming from the short focal length extremity to the long focal length extremity;

f 1 designates the focal length of said negative first lens group;

f 2 designates the focal length of said positive second lens group;

f 3 designates the focal length of said negative third lens group;

f 4 designates the focal length of said positive fourth lens group; and

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

9. A wide-angle zoom lens system comprising a negative first lensgroup, a positive second lens group, a negative third lens group and a positive fourth lensgroup, in this order from an object;

wherein upon zooming from the short focal length extremity to the long focallength extremity, a distance between said negative first lens group and said positive second lens group decreases, a distance between said positive second lens group and saidnegative third lens group increases, and a distance between said negative third lens group and said positive fourth lens group decreases; and

wherein said wide-angle zoom lens system satisfies the following conditions:

2.0< fBw×fBw /( f 1× f 3)<6.0

1.2< f 2/| f 1|<1.8

1.0< f 4/| f 3|<1.8

wherein

fBw designates the equivalent air thickness from the most image-side lenssurface to the image plane at the short focal length extremity;

f 1 designates the focal length of said negative first lens group;

f 2 designates the focal length of said positive second lens group;

f 3 designates the focal length of said negative third lens group; and

f 4 designates the focal length of said positive fourth lens group.

10. The wide-angle zoom lens system according to claim 9 , furthersatisfying the following conditions:

0.5< f 1/ f 3<0.9

0.6< f 2/ f 4<0.9

11. The wide-angle zoom lens system according to claim 9 , whereinsaid negative first lens group comprises a negative meniscus lens element having theconvex surface facing toward the object, another negative meniscus lens element havingthe convex surface facing toward the object, a negative lens element having a concavesurface facing toward an image and a positive lens element, in this order from the object.

12. The wide-angle zoom lens system according to claim 9 , whereinsaid negative first lens group comprises a positive lens element, a negative meniscus lenselement having the convex surface facing toward the object, another negative meniscuslens element having the convex surface facing toward the object, a negative lens elementhaving a concave surface facing toward an image and a positive lens element, in thisorder from the object.

13. The wide-angle zoom lens system according to claim 9 , whereinsaid positive second lens group comprises positive cemented lens elements and a positivelens element.

14. The wide-angle zoom lens system according to claim 9 , whereinsaid negative third lens group comprises negative cemented lens elements and a positivelens element, or, two sets of negative cemented lens elements.

15. The wide-angle zoom lens system according to claim 9 , whereinsaid positive fourth lens group comprises cemented lens elements and two positive lenselements.