Three-group zoom lens

1. A zoom lens formed of only three lens groups, arranged along an optical axis in order from the object side as follows:

a first lens group having negative refractive power;

a second lens group having positive refractive power and including a stop for controlling the amount of light that passes through the zoom lens;

a third lens group having positive refractive power;

wherein

during zooming from the wide-angle end to the telephoto end, the first lens group moves first toward the image side and then toward the object side, the second lens group moves monotonically toward the object side and closer to the first lens group, the third lens group moves first toward the object side and then toward the image side, and the second lens group moves farther from the third lens group;

with the zoom lens focused at infinity, the third lens group is closer to the object side at the wide-angle end than at the telephoto end;

when focusing from infinity to close range, the third lens group moves toward the object side; and

the following conditions are satisfied:

2.0<| f 1 |/f w <2.4

0.29 <f 2 /f 3 <0.37

 where

f w is the focal length of the entire zoom lens at the wide-angle end,

f 1 is the focal length of the first lens group,

f 2 is the focal length of the second lens group, and

f 3 is the focal length of the third lens group.

2. The zoom lens of claim 1 , wherein the following condition is satisfied:

2.7 <LT /( f w ·Z·tan ω)< 3.3

where

LT is the distance along the optical axis from the object-side surface of the first lens group to the image plane of the zoom lens at the telephoto end;

Z is the zoom ratio of the entire zoom lens, and

ω is the half-field angle at the wide-angle end.

3. The zoom lens of claim 1 , wherein the second lens group includes, arranged along the optical axis in order from the object side, a lens component that includes a biconvex lens element and a lens element having negative refractive power with its object-side surface concave and of greater curvature than its image-side surface, and a lens component having negative refractive power and having at least one aspheric surface.

4. The zoom lens of claim 3 , wherein said lens component that includes a biconvex lens element consists of two lens elements and said lens component having negative refractive power consists of a lens element.

5. The zoom lens of claim 3 , wherein the second lens group includes only three lens elements.

6. The zoom lens of claim 2 , wherein the second lens group includes, arranged along the optical axis in order from the object side, a lens component that includes a biconvex lens element and a lens element having negative refractive power with its object-side surface concave and of greater curvature than its image-side surface, and a lens component having negative refractive power and having at least one aspheric surface.

7. The zoom lens of claim 6 , wherein said lens component that includes a biconvex lens element consists of two lens elements and said lens component having negative refractive power consists of a lens element.

8. The zoom lens of claim 6 , wherein the second lens group includes only three lens elements.

9. The zoom lens of claim 1 , wherein the first lens group includes, arranged along the optical axis in order from the object side, a first lens component having negative refractive power, having at least one aspheric surface, and having a concave image-side surface of greater curvature than its object-side surface, and a second lens component having positive refractive power, having a meniscus shape, and having a convex object-side surface of greater curvature than its image-side surface.

10. The zoom lens of claim 9 , wherein each of said first lens component and said second lens components consists of a lens element.

11. The zoom lens of claim 9 , wherein the first lens group consists of two lens elements.

12. The zoom lens of claim 2 , wherein the first lens group includes, arranged along the optical axis in order from the object side, a first lens component having negative refractive power, having at least one aspheric surface, and having a concave image-side surface of greater curvature than its object-side surface, and a second lens component having positive refractive power, having a meniscus shape, and having a convex object-side surface of greater curvature than its image-side surface.

13. The zoom lens of claim 12 , wherein each of said first lens component and said second lens components consists of a lens element.

14. The zoom lens of claim 12 , wherein the first lens group consists of two lens elements.

15. The zoom lens of claim 1 , wherein the third lens group consists of a lens component having positive refractive power and having at least one aspheric surface.

16. The zoom lens of claim 15 , wherein the third lens group consists of a lens element.

17. The zoom lens of claim 2 , wherein the third lens group consists a lens component having positive refractive power and having at least one aspheric lens surface.

18. The zoom lens of claim 17 , wherein the third lens group consists of a lens element.

19. The zoom lens of claim 3 , wherein the third lens group consists of a lens component having positive refractive power and having at least one aspheric lens surface.

20. The zoom lens of claim 19 , wherein the third lens group consists of a lens element.