Imaging lens
An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; a fifth lens having negative refractive power; and a sixth lens. The 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. The fifth lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius. The sixth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens;
a fifth lens having negative refractive power; and
a sixth lens, arranged in this order from an object side to an image plane side,
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 fifth lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius, and
said sixth lens is formed in a meniscus shape so that a surface thereof on the object side near an optical axis thereof has a positive curvature radius.
2. 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, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, said fifth lens has an Abbe's number νd5, and said sixth lens has an Abbe's number νd6 so that the following conditional expressions are satisfied:
45<ν d 1<75
20<ν d 2<40
45<ν d 3<75
45<ν d 4<75
20<ν d 5<40
45<ν d 6<75.
3. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−1.0< f 56/ f<− 0.3
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
1.1< f 12/ f< 3.0
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
−0.8< f 1/ f 2<−0.3.
6. The imaging lens according to claim 1 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
1.0< f 3/ f< 5.0
where f is a focal length of a whole lens system.
7. 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:
−0.4< f 4/ f 5<−0.1.
8. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens;
a fifth lens having negative refractive power; and
a sixth lens, arranged in this order from an object side to an image plane side,
wherein said fifth lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius,
said sixth lens is formed in a meniscus shape so that a surface thereof on the object side have near an optical axis thereof has a positive curvature radius, and
said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−1.0< f 56/ f<− 0.3
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 8 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, said fifth lens has an Abbe's number νd5, and said sixth lens has an Abbe's number νd6 so that the following conditional expressions are satisfied:
45<ν d 1<75
20<ν d 2<40
45<ν d 3<75
45<ν d 4<75
20<ν d 5<40
45<ν d 6<75.
10. The imaging lens according to claim 8 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
1.1< f 12/ f< 3.0
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 f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
−0.8< f 1/ f 2<−0.3.
12. The imaging lens according to claim 8 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
1.0< f 3/ f< 5.0
where f is a focal length of a whole lens system.
13. The imaging lens according to claim 8 , 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:
−0.4< f 4/ f 5<−0.1.
14. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens;
a fifth lens having negative refractive power; and
a sixth lens, arranged in this order from an object side to an image plane side,
wherein said first 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 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 have negative curvature radii, and
said sixth lens is formed in a meniscus shape so that a surface thereof on the object side near an optical axis thereof has a positive curvature radius.
15. The imaging lens according to claim 14 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, said fifth lens has an Abbe's number νd5, and said sixth lens has an Abbe's number νd6 so that the following conditional expressions are satisfied:
45<ν d 1<75
20<ν d 2<40
45<ν d 3<75
45<ν d 4<75
20<ν d 5<40
45<ν d 6<75.
16. The imaging lens according to claim 14 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−1.0< f 56/ f<− 0.3
where f is a focal length of a whole lens system.
17. The imaging lens according to claim 14 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
1.1< f 12/ f< 3.0
where f is a focal length of a whole lens system.
18. The imaging lens according to claim 14 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
−0.8< f 1/ f 2<−0.3.
19. The imaging lens according to claim 14 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
1.0< f 3/ f< 5.0
where f is a focal length of a whole lens system.
20. The imaging lens according to claim 14 , 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:
−0.4< f 4/ f 5<−0.1.