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 having at least one aspheric surface; a fifth lens having at least one aspheric surface; a sixth lens having two aspheric surfaces; and a seventh lens having two aspheric surfaces, arranged in this order from an object side to an image plane side. The first lens is formed in a shape so that both surfaces are convex near an optical axis thereof. The fourth lens is formed in a meniscus shape so that a surface thereof on the object side is concave near the optical axis. The seventh lens is formed in a shape so that a surface thereof on the image plane side is concave near the optical axis.
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 at least one aspheric surface;
a fifth lens having at least one aspheric surface;
a sixth lens having two aspheric surfaces; and
a seventh lens having two aspheric surfaces, arranged in this order from an object side to an image plane side,
wherein said first lens is formed in a shape so that both surfaces are convex near an optical axis thereof,
said fourth lens is formed in a meniscus shape so that a surface thereof on the object side is concave near the optical axis, and
said seventh lens is formed in a shape so that a surface thereof on the image plane side is concave near the optical axis.
2. The imaging lens according to claim 1 , wherein said fourth lens has positive refractive power, and
said fifth lens has positive refractive power.
3. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
40<ν d 1<75,
20<ν d 2<35,
40<ν d 3<75,
40<ν d 4<75,
20 <νd 5<35.
4. The imaging lens according to claim 1 , wherein said sixth lens has negative refractive power,
said seventh lens has negative refractive power, and
said sixth lens has an Abbe's number νd6 and said seventh lens has an Abbe's number νd7 so that the following conditional expressions are satisfied:
20<ν d 6<35
40<ν d 7<75.
5. The imaging lens according to claim 1 , wherein said first lens has a focal length f1, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.3< f 3/ f 1<3.0.
6. The imaging lens according to claim 1 , wherein said second lens has a focal length f2, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.0< f 2/ f 3<−0.3.
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:
4.5< f 4/ f< 9.0
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 1 , wherein said third lens is disposed away from said fourth lens by a distance D34 on the optical axis so that the following conditional expression is satisfied:
0.05 <D 34 /f< 0.3
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 1 , wherein said fifth lens is disposed away from said sixth lens by a distance D56 on the optical axis so that the following conditional expression is satisfied:
0.05 <D 56 /f< 0.25
where f is a focal length of a whole lens system.
10. The imaging lens according to claim 1 , wherein said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
−4.0< f 7/ f<− 1.0
where f is a focal length of a whole lens system.
11. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having at least one aspheric surface;
a third lens having at least one aspheric surface;
a fourth lens having at least one aspheric surface;
a fifth lens having at least one aspheric surface;
a sixth lens having two aspheric surfaces; and
a seventh lens having negative refractive power and two aspheric surfaces, 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 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 near the optical axis, and
said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, and said fourth lens has an Abbe's number νd4 so that the following conditional expressions are satisfied:
40<ν d 1<75,
20<ν d 2<35,
40<ν d 4<75.
12. The imaging lens according to claim 11 , wherein said second lens has negative refractive power, and
said third lens has positive refractive power.
13. The imaging lens according to claim 11 , wherein said fourth lens has positive refractive power, and
said fifth lens has positive refractive power.
14. The imaging lens according to claim 11 , wherein said third lens has an Abbe's number νd3, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
40<ν d 3<75,
20<ν d 5<35.
15. The imaging lens according to claim 11 , wherein said sixth lens has negative refractive power,
said seventh lens has negative refractive power, and
said sixth lens has an Abbe's number νd6 and said seventh lens has an Abbe's number νd7 so that the following conditional expressions are satisfied:
20<ν d 6<35
40<ν d 7<75.
16. The imaging lens according to claim 11 , wherein said first lens has a focal length f1, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.3 <f 3 /f 1<3.0.
17. The imaging lens according to claim 11 , wherein said second lens has a focal length f2, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.0< f 2/ f 3<−0.3.
18. The imaging lens according to claim 11 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
4.5< f 4/ f< 9.0
where f is a focal length of a whole lens system.
19. The imaging lens according to claim 11 , wherein said fifth lens is disposed away from said sixth lens by a distance D56 on the optical axis so that the following conditional expression is satisfied:
0.05< D 56/ f< 0.25
where f is a focal length of a whole lens system.
20. The imaging lens according to claim 11 , wherein said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
−4.0< f 7/ f<− 1.0
where f is a focal length of a whole lens system.