Zoom lens

• US 6,898,023 B2
• Filed: 07/22/2003
• Issued: 05/24/2005
• Est. Priority Date: 07/22/2002
• Status: Expired due to Fees

• Current Assignee: Nidec Copal Corporation (Nidec Corporation)
• Original Assignee: Nidec Copal Corporation (Nidec Corporation)
• Inventors: Takeuchi, Hotaka
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US10/625,475
• Publication Number:
  US 20040125463A1
• Time in Patent Office: 672 Days
• Field of Search: 359676-692
• US Class Current: 359/689
• CPC Class Codes: G02B 13/0045 having five or more lenses
• CPC Class Codes: G02B 13/006 at least one element being a compound optical element, e.g. cemented elements
• CPC Class Codes: G02B 13/0065 having a beam-folding prism or mirror
• CPC Class Codes: G02B 13/009 having zoom function
• CPC Class Codes: G02B 15/143505 arranged --+

Abstract

The present invention provides a small, thin, light and low cost zoom lens suitable for cellular telephones, portable information terminals, etc. In particular, it can provide a small and thin, high performance zoom lens having a zoom ratio of approximately 2, a depth of less than 9 mm during shooting and in storage, a total lens length of less than 30 mm, an angle of view of approximately 61°, and a F number of approximately 2.8 providing a sufficient light, with various aberrations all suitably corrected.

Claims

1. A zoom lens comprising:

a first lens group having a negative refractive power as a whole,

a second lens group having a negative refractive power as a whole, and

a third lens group having a positive refractive power as a whole, arranged in said order from object side to image side, for zooming from a wide-angle end to a telephoto end by moving said third lens group from an image plane side to an object side as well as for correcting image plane changes required in accordance with said zooming by moving said second lens group;

wherein

said first lens group consists of a lens having a negative refractive power and a prism for changing a light path arranged in said order from the object side,

said second lens group consists of a lens having a negative refractive power; and

an aperture stop is provided between said second lens group and said third lens group.

2. A zoom lens claimed in claim 1 wherein,

said first lens group'"'"'s lens has an aspherical surface.

3. A zoom lens claimed in claim 2 wherein,

said aspherical surface is formed on a surface with a smaller curvature radius.

4. A zoom lens claimed in claim 3 wherein,

said aspherical surface is formed to have a weaker negative refractive power weakening toward its periphery.

5. A zoom lens claimed in claim 2 wherein,

said third lens group has at least one lens with a positive refractive power and at least one lens with a negative refractive power.

6. A zoom lens claimed in claim 2 wherein,

the prism of said first lens group is formed to have an entrance surface and an exit surface both oblong in a direction perpendicular to a plane that includes an entrance axis and an exit axis.

7. A zoom lens claimed in claim 2 that satisfies the following equations (1) and (2):

0.25<

|fw/f1|<

0.7, 

 

(1)

v1>

40, 

 

(2)

where

f1;

focal length of the first lens group,

fw;

focal length of the total lens system at the wide-angle end, and

v1;

Abbe number of the first lens group'"'"'s lens.

8. A zoom lens claimed in claim 2 that satisfies the following equation (3):

0.1<

f3/|f2<

0.8, 

 

(3)

where

f2;

focal length of the second lens group, and

f3;

focal length of the third lens group.

9. A zoom lens claimed in claim 1 wherein,

said third lens group has at least one lens with a positive refractive power and at least one lens with a negative refractive power.

10. A zoom lens claimed in claim 9 wherein,

said third lens group has a lens at a position closest to the object having a positive refractive power and an aspherical surface at least on one side.

11. A zoom lens claimed in claim 1 wherein,

the prism of said first lens group is formed to have an entrance surface and an exit surface both oblong in a direction perpendicular to a plane that includes an entrance axis and an exit axis.

12. A zoom lens claimed in claim 1 wherein, said first lens group'"'"'s lens has an aspherical surface.

13. A zoom lens claimed in claim 1 wherein,

said third lens group has at least one lens with a positive refractive power and at least one lens with a negative refractive power.

14. A zoom lens claimed in claim 1 wherein,

the prism of said first lens group is formed to have an entrance surface and an exit surface both oblong in a direction perpendicular to a plane that includes an entrance axis and an exit axis.

15. A zoom lens claimed in claim 1 that satisfies the following equations (1) and(2):

0.25<

|fw/f1|<

0.7, 

 

(1)

v1<

40, 

 

(2)

where

f1;

focal length of the first lens group,

fw;

focal length of the total lens system at the wide-angle end, and

v1;

Abbe number of the first lens group'"'"'s lens.

16. A zoom lens claimed in claim 1 that satisfies the following equation (3):

0.1<

f3/|f2|<

0.8, 

 

(3)

where

f2;

focal length of the second lens group, and

f3;

focal length of the third lens group.

17. A zoom lens claimed in claim 1, wherein the zoom lens comprises less than nine optical elements.

18. A zoom lens claimed in claim 1, wherein the zoom lens comprises less than seven lenses.

19. A zoom lens claimed in claim 1, wherein the prism of the first lens group is positioned adjacent to the lens of the first lens group and is positioned adjacent to the lens of the second lens group.

20. A zoom lens claimed in claim 1, wherein an exit surface of the prism at least partially faces the lens of the second lens group.

21. A zoom lens comprising:

a first lens group having a negative refractive power as a whole, a second lens group having a negative refractive power as a whole, and a third lens a group having a positive refractive power as a whole, arranged in said order from an object side to an image plane side, for zooming from a wide-angle end to a telephoto end by moving said third lens group from the image plane side to the object side as well as for correcting image plane changes required in accordance with said zooming by moving said second lens group;

wherein

said first lens group consists of a lens having a negative refractive power and a prism for changing a light path arranged in said order from the object side, and

said zoom lens satisfies the following equations (1) and (2);

0.25<

|fw/f1|<

0.7, 

 

(1)

v1<

40, 

 

(2)

where

f1;

focal length of the first lens group,

fw;

focal length of the total lens system at the wide-angle end, and

v1;

Abbe number of the first lens group'"'"'s lens.

22. A zoom lens claimed in claim 21 that satisfies the following equation (3):

0.1<

f3/|f2|<

0.8, 

 

(3)

where

f2;

focal length of the second lens group, and

f3;

focal length of the third lens group.

23. A zoom lens claimed in claim 21 that satisfies the following equation (3):

0.1<

f3/|f2|<

0.8, 

 

(3)

where

f2;

focal length of the second lens group, and

f3;

focal length of the third lens group.