Imaging lens
An imaging lens includes an aperture stop; a first lens having positive refractive power; a second lens having negative refractive power; 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. A surface of the first lens on the image plane side has a positive curvature radius. A surface of the third lens on the image plane side has a positive curvature radius. A surface of the fifth lens on the object side and a surface of the fifth lens on the image plane side have inflection points and are aspheric. A surface of the sixth lens on the object side has a positive curvature radius. The first to the third lenses have specific thicknesses so that specific conditional expressions are satisfied.
1. An imaging lens comprising:
an aperture stop;
a first lens having positive refractive power;
a second lens having negative refractive power;
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 image plane side has a positive curvature radius,
said third lens is formed in a shape so that a surface thereof on the image plane 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 inflection points and are aspheric,
said sixth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said first lens has a thickness T 1 on an optical axis thereof, said second lens has a thickness T 2 on an optical axis thereof, and said third lens has a thickness T 3 on an optical axis thereof so that the following conditional expressions are satisfied:
3.0< T 1/ T 2<4.0,
0.15< T 2/ T 3≤0.52,
and
said first lens is disposed away from the second lens by a distance D 12 on the optical axis, and said second lens is disposed away from the third lens by a distance D 23 on the optical axis so that the following conditional expression is satisfied:
3.38≤ D 23/ D 12<20.
2. 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:
−1.3< f 2/ f 3<−0.3.
3. 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:
0.5< f 3/ f< 3.0,
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said third lens has a focal length f 3 and said fourth lens has a focal length f 4 so that the following conditional expression is satisfied:
−1.0< f 3/ f 4<−0.01.
5. The imaging lens according to claim 1 , wherein said third lens is formed in a shape such that a surface thereof on the object side has a curvature radius R 3 f and a surface thereof on the image plane side has a curvature radius R 3 r so that the following conditional expression is satisfied:
−2.0< R 3 f/R 3 r< 0.6.
6. The imaging lens according to claim 1 , wherein said third lens is disposed away from the fourth lens by a distance D 34 on the optical axis, 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:
0.2< D 34/ D 45<2.0.
7. The imaging lens according to claim 1 , wherein said fourth lens has a thickness T 4 on an optical axis thereof so that the following conditional expression is satisfied:
0.7< T 3/ T 4<4.5.
8. The imaging lens according to claim 1 , wherein said fifth lens has a thickness T 5 on an optical axis thereof and said sixth lens has a thickness T 6 on an optical axis thereof so that the following conditional expression is satisfied:
0.6< T 5/ T 6<2.0.
9. The imaging lens according to claim 1 , wherein said third lens has an Abbe's number νd3 so that the following conditional expression is satisfied:
40<ν d 3<75.
10. The imaging lens according to claim 1 , wherein said fifth lens has an Abbe's number νd5 so that the following conditional expression is satisfied:
15<ν d 5<35.
11. An imaging lens comprising:
an aperture stop;
a first lens having positive refractive power;
a second lens having negative refractive power;
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 image plane side has a positive curvature radius,
said second lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius,
said third lens is formed in a shape so that a surface thereof on the image plane 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 inflection points and are aspheric,
said sixth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius, and
said first lens has a thickness T 1 on an optical axis thereof, said second lens has a thickness T 2 on an optical axis thereof, and said third lens has a thickness T 3 on an optical axis thereof so that the following conditional expressions are satisfied:
3.0< T 1/ T 2<4.0,
0.15< T 2/ T 3<0.6.
12. The imaging lens according to claim 11 , 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:
−1.3< f 2/ f 3<−0.3.
13. The imaging lens according to claim 11 , wherein said third lens has a focal length f 3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 3.0,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 11 , wherein said third lens has a focal length f 3 and said fourth lens has a focal length f 4 so that the following conditional expression is satisfied:
−1.0< f 3/ f 4<−0.01.
15. The imaging lens according to claim 11 , wherein said third lens is formed in a shape such that a surface thereof on the object side has a curvature radius R 3 f and the surface thereof on the image plane side has a curvature radius R 3 r so that the following conditional expression is satisfied:
−2.0< R 3 f/R 3 r< 0.6.
16. The imaging lens according to claim 11 , wherein said third lens is disposed away from the fourth lens by a distance D 34 on the optical axis, 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:
0.2< D 34/ D 45<2.0.
17. The imaging lens according to claim 11 , wherein said fourth lens has a thickness T 4 on an optical axis thereof so that the following conditional expression is satisfied:
0.7< T 3/ T 4<4.5.
18. The imaging lens according to claim 11 , wherein said fifth lens has a thickness T 5 on an optical axis thereof and said sixth lens has a thickness T 6 on an optical axis thereof so that the following conditional expression is satisfied:
0.6< T 5/ T 6<2.0.
19. The imaging lens according to claim 11 , wherein said third lens has an Abbe's number νd3 so that the following conditional expression is satisfied:
40<ν d 3<75.
20. The imaging lens according to claim 11 , wherein said fifth lens has an Abbe's number νd5 so that the following conditional expression is satisfied:
15<ν d 5<35.