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; and a sixth lens, arranged in this order from an object side to an image plane side. The second lens is formed in a shape so that an entire surface thereof on the object side is convex. The fifth lens is formed in a shape so that a surface thereof on the object side is convex toward the object side near an optical axis thereof, and a surface thereof on the image plane side is convex toward the image plane side near the optical axis thereof. The fourth lens has a specific Abbe's number.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
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 imaging lens has a total of six single lenses,
said first lens, said second lens, said third lens, said fourth lens, said fifth lens, and said sixth lens are arranged respectively with a space in between,
said second lens is formed in a shape so that an entire surface thereof on the object side is convex,
said fifth lens is formed in a shape so that a surface thereof on the object side is convex toward the object side near an optical axis thereof, and a surface thereof on the image plane side is convex toward the image plane side near the optical axis thereof,
said sixth lens is formed in a shape so that a surface thereof on the image plane side is concave toward the image plane side near an optical axis thereof, and
said fourth lens has an Abbe's number νd4 so that the following conditional expression is satisfied:
20<ν d 4<40.
2. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number vdl, said second lens has an Abbe's number νd2, and said third lens has an Abbe's number νd3 so that the following conditional expressions are satisfied:
45<ν d 1<75,
20<ν d 2<40,
45<ν d 3<75.
3. The imaging lens according to claim 1 , wherein said fourth lens is formed in a shape so that a surface thereof on the image plane side is convex toward the image plane side on an optical axis thereof.
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:
−1.5< f 1/ f 2<−0.4.
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:
0.5< f 3/ f< 2.0
where f is a focal length of a whole lens system.
6. The imaging lens according to claim 1 , wherein said second lens is formed in the shape so that the surface thereof on the object side has a curvature radius R2f and a surface thereof on the image plane side has a curvature radius R2r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
7. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0< f 4/ f<− 1.0
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 1 , wherein said fifth lens has a focal length f5 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−2.0< f 5/ f 6<−0.5.
9. The imaging lens according to claim 1 , wherein 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 5<75,
45<ν d 6<75.
10. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens;
a fifth lens having positive 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 is convex toward the object side near an optical axis thereof,
said second lens is formed in a shape so that an entire surface thereof on the object side is convex,
said fifth lens is formed in a shape so that a surface thereof on the object side has an aspheric shape having an inflection point, and a surface thereof on the image plane side is convex toward the image plane side near an optical axis thereof,
said sixth lens is formed in a shape so that a surface thereof on the image plane side is concave toward the image plane side near an optical axis thereof, and
said third lens has an Abbe's number νd3 so that the following conditional expression is satisfied:
45<ν d 3<75.
11. The imaging lens according to claim 10 , wherein said first lens has an Abbe's number νd1 and said second lens has an Abbe's number νd2 so that the following conditional expressions are satisfied:
45<ν d 1<75,
20<ν d 2<40.
12. The imaging lens according to claim 10 , wherein said fourth lens is formed in a shape so that a surface thereof on the image plane side is convex toward the image plane side on an optical axis thereof.
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:
−1.5< f 1/ f 2<−0.4.
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:
0.5< f 3/ f< 2.0
where f is a focal length of a whole lens system.
15. The imaging lens according to claim 10 , wherein said second lens is formed in the shape so that the surface thereof on the object side has a curvature radius R2f and a surface thereof on the image plane side has a curvature radius R2r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
16. The imaging lens according to claim 10 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0< f 4/ f<− 1.0
where f is a focal length of a whole lens system.
17. The imaging lens according to claim 10 , wherein said fifth lens has a focal length f5 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−2.0< f 5/ f 6<−0.5.
18. The imaging lens according to claim 10 , wherein 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 5<75,
45<ν d 6<75.