Imaging lens
An imaging lens includes a first lens; 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 first lens has a surface thereof on the object side having a positive curvature radius. The second lens has surfaces on the object side and the image plane side having positive curvature radii. The third lens has a surface on the object side having a positive curvature radius and a surface on the image plane side having a negative curvature radius. The fifth lens is formed has an aspheric shape surface on the object side. The sixth lens has an aspheric shape surface on the image plane side. The first to fourth lenses have refractive power weaker than that of the fifth and sixth lenses.
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 having negative refractive power;
a fifth lens having positive 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 first lens is formed in a shape so that an object side surface thereof is convex toward the object side near an optical axis thereof,
said second lens is formed in a meniscus shape so that an object side surface thereof is convex toward the object side near an optical axis thereof,
said third lens is formed in a shape so that an object side surface thereof is convex toward the object side near an optical axis thereof, and an image plane side surface thereof is convex toward the image plane side near the optical axis thereof,
said fourth lens is formed in a meniscus shape so that an object side surface thereof is concave toward the object side near an optical axis thereof, and an image plane side surface thereof is convex toward the image plane side near the optical axis thereof,
said fifth lens is formed in a shape so that an object side surface thereof has an aspheric shape having an inflexion point,
said sixth lens is formed in a shape so that an image plane side surface thereof has an aspheric shape having an inflexion point, and
each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens.
2. The imaging lens according to claim 1 , wherein said first lens has a focal length f 1 and said second lens has a focal length f 2 so that the following conditional expression is satisfied:
−1.5< f 1/ f 2<−0.4.
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< 2.0
where f is a focal length of a whole lens system.
4. 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 R 2 f and the surface thereof on the image plane side has a curvature radius R 2 r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
5. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f 4 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.
6. The imaging lens according to claim 1 , wherein said fifth lens has a focal length f 5 and said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−2.0< f 5/ f 6<−0.5.
7. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number νd 1 , said third lens has an Abbe's number νd 3 , said fifth lens has an Abbe's number νd 5 , and said sixth lens has an Abbe's number νd 6 so that the following conditional expressions are satisfied:
45<ν d 1<75
45<ν d 3<75
45<ν d 5<75
45<ν d 6<75.
8. The imaging lens according to claim 1 , wherein said second lens has an Abbe's number νd 2 and said fourth lens has an Abbe's number νd 4 so that the following conditional expressions are satisfied:
20<ν d 2<40
20<ν d 4<40.
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 having negative refractive power;
a fifth lens having positive 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 first lens is formed in a shape so that an object side surface thereof is convex toward the object side near an optical axis thereof,
said second lens is formed in a meniscus shape so that an object side surface thereof is convex toward the object side near an optical axis thereof,
said third lens is formed in a shape so that an object side surface thereof is convex toward the object side near an optical axis thereof, and an image plane side surface thereof is convex toward the image plane side near the optical axis thereof,
said fourth lens is formed in a meniscus shape so that an object side surface thereof is concave toward the object side near an optical axis thereof, and an image plane side surface thereof is convex toward the image plane side near the optical axis thereof,
said fifth lens is formed in a shape so that an object side surface thereof has an aspheric shape having an inflexion point,
said sixth lens is formed in a shape so that an image plane side surface thereof has an aspheric shape having an inflexion point,
each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens,
said second lens is formed in the shape so that the surface thereof on the object side has a curvature radius R 2 f and the surface thereof on the image plane side has a curvature radius R 2 r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8, and
said fourth lens has a focal length f 4 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.
10. The imaging lens according to claim 9 , wherein said fourth lens is formed in a meniscus shape so that an object side surface thereof is concave toward the object side near an optical axis thereof.
11. The imaging lens according to claim 9 , wherein said first lens has a focal length f 1 and said second lens has a focal length f 2 so that the following conditional expression is satisfied:
−1.5< f 1/ f 2<−0.4.
12. The imaging lens according to claim 9 , wherein said third lens has a focal length f 3 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.
13. The imaging lens according to claim 9 , wherein said fifth lens has a focal length f 5 and said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−2.0< f 5/ f 6<−0.5.
14. The imaging lens according to claim 9 , wherein said first lens has an Abbe's number νd 1 , said third lens has an Abbe's number νd 3 , said fifth lens has an Abbe's number νd 5 , and said sixth lens has an Abbe's number νd 6 so that the following conditional expressions are satisfied:
45<ν d 1<75
45<ν d 3<75
45<ν d 5<75
45<ν d 6<75.
15. The imaging lens according to claim 9 , wherein said second lens has an Abbe's number νd 2 and said fourth lens has an Abbe's number νd 4 so that the following conditional expressions are satisfied:
20<ν d 2<40
20<ν d 4<40.