Imaging lens
An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens; a fifth lens having negative refractive power; and a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side. The sixth lens is formed in a shape so that a surface on the object side and a surface on the image plane side have negative curvature radii. The first lens has a specific focal length, the second lens has a specific focal length, the fourth lens is arranged to be away from the fifth lens by a specific distance on an optical axis, and the surface of the sixth lens on the image plane side has a specific curvature radius so that specific conditional expressions are satisfied.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having positive refractive power;
a fourth lens;
a fifth lens having negative refractive power; and
a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said third lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is negative,
said fifth lens is formed in a shape so that a curvature radius of a surface thereof on the object side is negative,
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, and
said first lens has a focal length f1, said second lens has a focal length f2, said fourth lens is arranged to be away from the fifth lens by a distance D45 on an optical axis thereof, and said sixth lens is formed in the shape so that the surface thereof on the image plane side has a curvature radius R6r so that the following conditional expressions are satisfied:
f 1<| f 2|
0.02< D 45/ f< 0.5
−80< R 6 r/f<− 5
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said sixth lens is formed in a shape so that a surface thereof on the object side has a curvature radius R6f and a surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
3< |R 6 r/R 6 f |<150.
3. 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:
−1.0< f 1/ f 2<−0.1.
4. 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< f 3/ f< 5.
5. 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:
−2.0< f 56/ f<− 0.1.
6. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.0< f 6/ f<− 0.5.
7. The imaging lens according to claim 1 , wherein said third lens is formed in a shape so that a surface thereof on the image plane side has an effective diameter Φ3, and said sixth lens is formed in the shape so that the surface thereof on the image plane side has an effective diameter Φ6 so that the following conditional expression is satisfied:
1.5<Φ6/Φ3<3.
8. The imaging lens according to claim 1 , wherein said second lens is arranged to be away from the third lens by a distance D23 on an optical axis thereof so that the following conditional expression is satisfied:
0.01< D 23/ f< 0.5.
9. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having positive refractive power;
a fourth lens;
a fifth lens having negative refractive power; and
a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said third lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is negative,
said fifth lens is formed in a shape so that a curvature radius of a surface thereof on the object side is negative,
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, and
said fourth lens is arranged to be away from the fifth lens by a distance D45 on an optical axis thereof, said first lens is arranged so that a surface thereof on the object side is away from an image plane by a distance La on an optical axis thereof, and said imaging lens has an angle of view 2ω so that the following conditional expressions are satisfied:
0.02< D 45/ f< 0.5
1.2< La/H max<1.8
70°≤2ω
where f is a focal length of a whole lens system and Hmax is a maximum image height of the image plane.
10. The imaging lens according to claim 9 , wherein said sixth lens is formed in a shape so that a surface thereof on the object side has a curvature radius R6f and a surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
3<| R 6 r/R 6 f|< 150.
11. The imaging lens according to claim 9 , 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:
−1.0< f 1/ f 2<−0.1.
12. The imaging lens according to claim 9 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
1< f 3/ f< 5.
13. The imaging lens according to claim 9 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−2.0< f 56/ f<− 0.1.
14. The imaging lens according to claim 9 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.0< f 6/ f<− 0.5.
15. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having positive refractive power;
a fourth lens having positive refractive power;
a fifth lens having negative refractive power; and
a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said third lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive and a curvature radius of a surface thereof on the image plane side is negative,
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, and
said first lens has a focal length f1, said second lens has a focal length f2, said fourth lens is arranged to be away from the fifth lens by a distance D45 on an optical axis thereof so that the following conditional expressions are satisfied:
f 1<| f 2|
0.05< D 45/ f< 0.5
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 15 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
0.5< f 4/ f< 5.0.
17. The imaging lens according to claim 15 , wherein said third lens has a focal length f3 and said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
0.5< f 3/ f 4<4.5.
18. The imaging lens according to claim 15 , wherein said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expression is satisfied:
2< f 45/ f< 8.
19. The imaging lens according to claim 15 , wherein said first lens is arranged so that a surface thereof on the object side is away from an image plane by a distance La on an optical axis thereof so that the following conditional expression is satisfied:
1.2< La/H max<1.8
where Hmax is a maximum image height of the image plane.