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