Imaging lens
An imaging lens includes a first lens group and a second lens group, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens having at least one aspheric surface, and a third lens having at least one aspheric surface, arranged with a space in between. The second lens group includes a fourth lens having at least one aspheric surface, a fifth lens having negative refractive power and two aspheric surfaces, and a sixth lens having negative refractive power and two aspheric surfaces, arranged with a space in between. The sixth lens is formed in a shape so that a curvature radius of the surface on the object side is negative near an optical axis. The first lens has a specific focal length so that a specific conditional expression is satisfied.
1. An imaging lens comprising:
a first lens group; and
a second lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens having positive refractive power, a second lens having at least one aspheric surface, and a third lens having at least one aspheric surface, arranged with a space in between,
said second lens group includes a fourth lens having at least one aspheric surface, a fifth lens having negative refractive power and two aspheric surfaces, and a sixth lens having negative refractive power and two aspheric surfaces, arranged with a space in between,
said sixth lens is formed in a shape so that a curvature radius of the surface thereof on the object side is negative near an optical axis thereof, and
said first lens has a focal length f1 so that the following conditional expression is satisfied:
10< f 1 /f< 40
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said third lens is formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are positive near an optical axis thereof.
3. The imaging lens according to claim 1 , wherein said fifth lens is formed in a shape so that a curvature radius of the surface thereof on the image plane side is positive near an optical axis thereof.
4. The imaging lens according to claim 1 , wherein said sixth lens is formed in the shape so that a curvature radius of the surface thereof on the image plane side is negative near the optical axis thereof.
5. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, and said third lens has an Abbe's number νd3 so that the following conditional expressions are satisfied:
40<ν d 1<75
40<ν d 2<75
15<ν d 3<35.
6. The imaging lens according to claim 1 , wherein said second lens has a focal length f2 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−5< f 3 /f 2<−1.
7. The imaging lens according to claim 1 , wherein said first lens group has a focal length F1 and said second lens group has a focal length F2 so that the following conditional expression is satisfied:
−12< F 2 /F 1<−1.5.
8. The imaging lens according to claim 1 , wherein said third lens is arranged away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.1< D 34 /f< 0.4.
9. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 and said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−15< f 5 /f 4<−5.
10. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.5< f 6 /f<− 0.5.
11. An imaging lens comprising:
a first lens group; and
a second lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens, a second lens having positive refractive power and at least one aspheric surface, and a third lens having at least one aspheric surface, arranged with a space in between,
said second lens group includes a fourth lens having at least one aspheric surface, a fifth lens having negative refractive power and two aspheric surfaces, and a sixth lens having negative refractive power and two aspheric surfaces, arranged with a space in between,
said sixth lens is formed in a shape so that a curvature radius of the surface thereof on the object side is negative near an optical axis thereof, and
said second lens has a focal length f2 so that the following conditional expression is satisfied:
0.3< f 2 /f< 0.9
where f is a focal length of a whole lens system.
12. The imaging lens according to claim 11 , wherein said third lens is formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are positive near an optical axis thereof.
13. The imaging lens according to claim 11 , wherein said sixth lens is formed in the shape so that a curvature radius of the surface thereof on the image plane side is negative near the optical axis thereof.
14. The imaging lens according to claim 11 , wherein said first lens has a focal length f1 so that the following conditional expression is satisfied:
10< f 1 /f< 40.
15. The imaging lens according to claim 11 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, and said third lens has an Abbe's number νd3 so that the following conditional expressions are satisfied:
40<ν d 1<75
40<ν d 2<75
15<ν d 3<35.
16. The imaging lens according to claim 11 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
−5< f 3 /f 2<−1.
17. The imaging lens according to claim 11 , wherein said first lens group has a focal length F1 and said second lens group has a focal length F2 so that the following conditional expression is satisfied:
−12< F 2 /F 1<−1.5.
18. The imaging lens according to claim 11 , wherein said third lens is arranged away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.1< D 34 /f< 0.4.
19. The imaging lens according to claim 11 , wherein said fourth lens has a focal length f4 and said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−15< f 5 /f 4<−5.
20. The imaging lens according to claim 11 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.5< f 6 /f<− 0.5.