High zoom-ratio zoom lens system

1. A high zoom-ratio zoom lens system of five lens groups comprises a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a negative fifth 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 positive first lens group and said negative second lens group increases, and a distance between said negative second lens group and said positive third lens group decreases; and

wherein said high zoom-ratio zoom lens system satisfies the following conditions:

5.5< f 1/| f 2|<10.0( f 2<0)

1.7< f 3/ f 4<4.0

wherein

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

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

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

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

2. The high zoom-ratio zoom lens system according to claim 1 , satisfying the following conditions:

4.5< f 1/ fw< 10.0

1.4< fBw/fw< 2.0

wherein

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

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

fBw designates the back focal distance at the short focal length extremity.

3. The high zoom-ratio zoom lens system according to claim 1 , satisfying the following conditions:

0.4< Z 2/ Z< 0.6

wherein

Z designates the zoom ratio of the entire zoom lens system (=ft/fw);

Z 2 designates the zoom ratio of said negative second lens group (=m 2 t /m 2 w );

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

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

m 2 w designates the lateral magnification of said negative second lens group at the short focal length extremity; and

m 2 t designates the lateral magnification of said negative second lens group at the long focal length extremity.

4. The high zoom-ratio zoom lens system according to claim 1 , wherein said negative second lens group comprises a negative lens element, cemented lens elements having a negative lens element and a positive lens element, and cemented lens elements having a negative lens element and a positive lens element, in this order from the object.

5. The high zoom-ratio zoom lens system according to claim 1 , wherein said negative fifth lens group functions as a focusing lens group; and

wherein said high zoom-ratio zoom lens system preferably satisfies the following conditions:

2.2<m5t<3.5

2.0< f 5/ f 2<5.0

wherein

m 5 t designates the lateral magnification of said negative fifth lens group at the long focal length extremity;

f 5 designates the focal length of said negative fifth lens group; and

f 2 designates the focal length of said negative second lens group.

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

1.5<| f 5|/ fw< 4.5( f 5<0)

wherein

f 5 designates the focal length of said negative fifth lens group; and

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

7. The high zoom-ratio zoom lens system according to claim 5 , wherein said negative fifth lens group comprises a negative lens element, a negative lens element and a positive lens element, in this order from the object.

8. A high zoom-ratio zoom lens system of five lens groups comprises a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a negative fifth 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 positive first lens group and said negative second lens group increases, and a distance between said negative second lens group and said positive third lens group decreases; and

wherein said high zoom-ratio zoom lens system satisfies the following conditions:

4.5< f 1/ fw< 10.0

1.4< fBw/fw< 2.0

wherein

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

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

fBw designates the back focal distance at the short focal length extremity.

9. The high zoom-ratio zoom lens system according to claim 8 , satisfying the following conditions:

0.4< Z 2/ Z< 0.6

wherein

Z designates the zoom ratio of the entire zoom lens system (=ft/fw);

Z 2 designates the zoom ratio of said negative second lens group (=m 2 t /m 2 w );

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

m 2 w designates the lateral magnification of said negative second lens group at the short focal length extremity; and

m 2 t designates the lateral magnification of said negative second lens group at the long focal length extremity.

10. The high zoom-ratio zoom lens system according to claim 8 , wherein said negative second lens group comprises a negative lens element, cemented lens elements having a negative lens element and a positive lens element, and cemented lens elements having a negative lens element and a positive lens element, in this order from the object.

11. The high zoom-ratio zoom lens system according to claim 8 , wherein said negative fifth lens group functions as a focusing lens group; and

wherein said high zoom-ratio zoom lens system preferably satisfies the following conditions:

2.2<m5t<3.5

2.0< f 5/ f 2<5.0

wherein

m 5 t designates the lateral magnification of said negative fifth lens group at the long focal length extremity;

f 5 designates the focal length of said negative fifth lens group; and

f 2 designates the focal length of said negative second lens group.

12. The high zoom-ratio zoom lens system according to claim 11 , satisfying the following condition:

1.5<| f 5|/ fw< 4.5( f 5<0)

wherein

f 5 designates the focal length of said negative fifth lens group; and

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

13. The high zoom-ratio zoom lens system according to claim 11 , wherein said negative fifth lens group comprises a negative lens element, a negative lens element and a positive lens element, in this order from the object.

14. A high zoom-ratio zoom lens system comprises a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in this order from the object,

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

wherein said high zoom-ratio zoom lens system satisfies the following conditions:

5.5< f 1/| f 2|<10.0( f 2<0)

1.7< f 3/ f 4<4.0

4.5< f 1/ fw< 10.0

1.4< fBw/fw< 2.0

wherein

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

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

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

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

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

fBw designates the back focal distance at the short focal length extremity.

15. The high zoom-ratio zoom lens system according to claim 14 , satisfying the following conditions:

0.4< Z 2/ Z< 0.6

wherein

Z designates the zoom ratio of the entire zoom lens system (=ft/fw);

Z 2 designates the zoom ratio of said negative second lens group (=m 2 t /m 2 w );

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

m 2 w designates the lateral magnification of said negative second lens group at the short focal length extremity; and

m 2 t designates the lateral magnification of said negative second lens group at the long focal length extremity.

16. The high zoom-ratio zoom lens system according to claim 14 , wherein said negative second lens group comprises a negative lens element, cemented lens elements having a negative lens element and a positive lens element, and cemented lens elements having a negative lens element and a positive lens element, in this order from the object.

17. A high zoom-ratio zoom lens system of five lens groups comprises a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a negative fifth lens group, in this order from an object,

wherein focusing is performed by moving said negative fifth lens group in the optical axis direction; and

wherein said high zoom-ratio zoom lens system satisfies the following conditions:

2.2<m5t<3.5

2.0< f 5/ f 2<5.0

wherein

m 5 t designates the lateral magnification of said negative fifth lens group at the long focal length extremity;

f 5 designates the focal length of said negative fifth lens group; and

f 2 designates the focal length of said negative second lens group.

18. The high zoom-ratio zoom lens system according to claim 17 , satisfying the following condition:

1.5<| f 5|/ fw< 4.5( f 5<0)

wherein

f 5 designates the focal length of said negative fifth lens group; and

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

19. The high zoom-ratio zoom lens system according to claim 17 , wherein said negative fifth lens group comprises a negative lens element, a negative lens element and a positive lens element, in this order from the object.

20. The high zoom-ratio zoom lens system according to claim 17 , wherein said negative second lens group comprises a negative lens element, cemented lens elements having a negative lens element and a positive lens element, and cemented lens elements having a negative lens element and a positive lens element, in this order from the object.