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, a second lens having positive refractive power, and a third lens. The second lens group includes a fourth lens, a fifth lens, and a sixth lens. The third lens and the fourth lens are arranged in a specific configuration.
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, a second lens having positive refractive power, and a third lens, arranged with a space in between,
said second lens group includes a fourth lens, a fifth lens, and a sixth lens, arranged with a space in between,
said first 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,
said third lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is positive near an optical axis thereof,
said third lens is formed in the shape so that a surface thereof on the object side and the surface thereof on the image plane side are aspheric,
said fourth lens is formed in a shape so that a curvature radius of a surface thereof on the object side is negative near an optical axis thereof,
said fifth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric,
said sixth 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 negative near an optical axis thereof,
said sixth lens is formed in the shape so that the surface thereof on the object side and the surface thereof on the image plane side are aspheric, and
said third lens is arranged away from the fourth lens by a distance D 34 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.
2. The imaging lens according to claim 1 , wherein said first lens group has positive refractive power, and
said second lens group has negative refractive power.
3. The imaging lens according to claim 1 , wherein said first lens has positive refractive power.
4. The imaging lens according to claim 1 , wherein said third lens has negative refractive power.
5. The imaging lens according to claim 1 , wherein said fourth lens has positive refractive power.
6. The imaging lens according to claim 1 , wherein said sixth lens has negative refractive power.
7. 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 object side is positive near an optical axis thereof, and a curvature radius of a surface thereof on the image plane side is negative near the optical axis thereof.
8. The imaging lens according to claim 1 , wherein said third lens is formed in the shape so that a curvature radius of the surface thereof on the object side is positive near the optical axis thereof.
9. The imaging lens according to claim 1 , wherein said fourth lens is formed in the shape so that a curvature radius of a surface thereof on the image plane side is negative near the optical axis thereof.
10. The imaging lens according to claim 1 , wherein said fifth lens is formed in the 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.
11. The imaging lens according to claim 1 , wherein said first lens has a focal length f 1 , said first lens has an Abbe's number νd 1 , said second lens has an Abbe's number νd 2 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
10< f 1/ f< 40
40<ν d 1<75
40<ν d 2<75
15<ν d 3<35.
12. The imaging lens according to claim 1 , wherein said second lens has a focal length f 2 , and said third lens has a focal length f 3 so that the following conditional expression is satisfied:
−5< f 3/ f 2<−1.
13. The imaging lens according to claim 1 , wherein said first lens group has a focal length F 1 and said second lens group has a focal length F 2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
14. The imaging lens according to claim 1 , wherein said fifth lens has negative refractive power, and
said fourth lens has a focal length f 4 and said fifth lens has a focal length f 5 so that the following conditional expression is satisfied:
−15< f 5/ f 4<−5.
15. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens have a composite focal length f 56 so that the following conditional expression is satisfied:
−3< f 56/ f<− 0.8.