Imaging lens
An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having negative refractive power; a fourth lens; a fifth lens; and a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side. The fourth lens and the fifth lens have a composite focal length f 45 , and the third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied: 0< f 45, 40<ν d 3<75.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having negative refractive power;
a fourth lens;
a fifth lens formed of one single lens and having positive refractive power; and
a sixth lens formed of one single lens and having negative refractive power, arranged in this order from an object side to an image plane side with a space in between,
wherein said second lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said third lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said fifth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius,
said sixth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said fourth lens and said fifth lens have a composite focal length f 45 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
0< f 45,
40<ν d 3<75.
2. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have the composite focal length f 45 so that the following conditional expression is satisfied:
0.5< f 45/ f< 2.5
where f is a focal length of a whole lens system.
3. The imaging lens according to claim 1 , wherein said first lens has a focal length f 1 , and said second lens and said third lens have a composite focal length f 23 so that the following conditional expression is satisfied:
−1.2< f 1/ f 23<−0.2.
4. The imaging lens according to claim 1 , wherein said third lens has a focal length f 3 so that the following conditional expression is satisfied:
−30< f 3/ f<− 10
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−2.0< f 6/ f<− 0.5
where f is a focal length of a whole lens system.
6. The imaging lens according to claim 1 , wherein said fourth lens is disposed away from the fifth lens by a distance D 45 on an optical axis thereof so that the following conditional expression is satisfied:
0.05< D 45/ f< 0.2
where f is a focal length of a whole lens system.
7. The imaging lens according to claim 1 , wherein
said fifth lens has a focal length f 5 and said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−6.0< f 5/ f 6<−1.5.
8. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having negative refractive power;
a fourth lens;
a fifth lens formed of one single lens; and
a sixth lens formed of one single lens and having negative refractive power, arranged in this order from an object side to an image plane side with a space in between,
wherein said first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said third lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said fourth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius and a surface thereof on the image plane side has a negative curvature radius,
said sixth lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius, and
said fourth lens is disposed away from the fifth lens by a distance D 45 on an optical axis thereof so that the following conditional expression is satisfied:
0.08 ≦D 45/ f< 0.2
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 8 , wherein said fourth lens and said fifth lens have a composite focal length f 45 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
0< f 45,
40<ν d 3<75.
10. The imaging lens according to claim 8 , wherein said fourth lens and said fifth lens have a composite focal length f 45 so that the following conditional expression is satisfied:
0.5< f 45/ f< 2.5
where f is a focal length of a whole lens system.
11. The imaging lens according to claim 8 , wherein said first lens has a focal length f 1 , and said second lens and said third lens have a composite focal length f 23 so that the following conditional expression is satisfied:
−1.2< f 1 /f 23<−0.2.
12. The imaging lens according to claim 8 , wherein said third lens has a focal length f 3 so that the following conditional expression is satisfied:
−30< f 3/ f<− 10.
13. The imaging lens according to claim 8 , wherein said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−2.0< f 6/ f<− 0.5.
14. The imaging lens according to claim 8 , wherein said fifth lens has positive refractive power, and
said fifth lens has a focal length f 5 and said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−6.0< f 5/ f 6<−1.5.
15. The imaging lens according to claim 8 , wherein said fifth lens has negative refractive power, and
said fifth lens has a focal length f 5 and said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
5< f 5/ f 6<20.