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 positive refractive power, 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 positive refractive power and at least one aspheric surface, a fifth lens having two aspheric surfaces, and a sixth lens having 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 thereof on the image plane side is negative near an optical axis thereof.
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 positive refractive power, 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 positive refractive power and at least one aspheric surface, a fifth lens having two aspheric surfaces, and a sixth lens having two aspheric surfaces, arranged with a space in between, and
said sixth lens is formed in a shape so that a curvature radius of the surface thereof on the image plane side is negative near an optical axis thereof.
2. The imaging lens according to claim 1 , wherein said second lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is negative near an optical axis thereof.
3. 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.
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 object side is negative near the optical axis thereof.
5. The imaging lens according to claim 1 , wherein 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.
6. The imaging lens according to claim 1 , wherein 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.
7. 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.
8. 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.
9. The imaging lens according to claim 1 , wherein said third lens is arranged away from the fourth lens by a distance D34 on the optical axis so that the following conditional expression is satisfied:
0.1< D 34/ f< 0.4
where f is a focal length of a whole lens system.
10. 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.
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 having positive refractive power, a second lens having positive refractive power, 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 two aspheric surfaces, arranged with a space in between, and
said sixth lens is formed in a shape so that a curvature radius of the surface thereof on the image plane side is negative near an optical axis thereof.
12. The imaging lens according to claim 11 , wherein said second lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is negative near an optical axis thereof.
13. 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.
14. 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 object side is negative near the optical axis thereof.
15. 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
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 11 , wherein 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.
17. The imaging lens according to claim 11 , 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.
18. 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.
19. The imaging lens according to claim 11 , wherein said third lens is arranged away from the fourth lens by a distance D34 on the optical axis so that the following conditional expression is satisfied:
0.1< D 34/ f< 0.4
where f is a focal length of a whole lens system.
20. 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.