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 at least one aspheric surface, and a third lens having two aspheric surfaces, arranged with a space in between. The second lens group includes a fourth lens having two aspheric surfaces, 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. The third lens is arranged away from the fourth lens by a specific distance, and the fifth lens and the sixth lens have a specific composite focal length, so that specific conditional expressions are 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 positive refractive power and at least one aspheric surface, and a third lens having two aspheric surfaces, arranged with a space in between,
said second lens group includes a fourth lens having two aspheric surfaces, 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 third lens is arranged away from the fourth lens by a distance D34 on an optical axis thereof, and said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expressions are satisfied:
0.1< D 34/ f< 0.4
−3< f 56/ f<− 0.8
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 the surface thereof on the object side and a curvature radius of the 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 a shape so that a curvature radius of the surface thereof on the image plane side is negative near an 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.
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.
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 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 having positive refractive power, a second lens having positive refractive power and at least one aspheric surface, and a third lens having two aspheric surfaces, arranged with a space in between,
said second lens group includes a fourth lens having two aspheric surfaces, 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,
said third lens is formed in a shape so that a curvature radius of the surface thereof on the object side and a curvature radius of the surface thereof on the image plane side are positive near an optical axis thereof, and
said first lens group has a focal length F1 so that the following conditional expression is satisfied:
0.7< F 1/ f≦ 1.13
where f is a focal length of a whole lens system.
12. The imaging lens according to claim 11 , 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.
13. The imaging lens according to claim 11 , wherein 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.
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 second lens has a focal length f2 so that the following conditional expression is satisfied:
0.3< f 2/ f< 0.9.
16. 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.
17. The imaging lens according to claim 11 , wherein 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.