Imaging lens
An imaging lens includes a first lens; a second lens; a third lens having negative refractive power; a fourth lens having positive refractive power; a fifth lens; a sixth lens; and a seventh lens, arranged in this order from an object side to an image plane side. The first lens has at least one aspheric surface. The fifth lens has two aspheric surfaces. The sixth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof and a surface thereof on the image plane side is concave at a paraxial region thereof. The seventh lens has two aspheric surfaces.
1. An imaging lens comprising:
a first lens;
a second lens;
a third lens having negative refractive power;
a fourth lens having positive refractive power;
a fifth lens;
a sixth lens; and
a seventh lens, arranged in this order from an object side to an image plane side,
wherein said first lens has at least one aspheric surface,
said fifth lens has two aspheric surfaces,
said sixth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof and a surface thereof on the image plane side is concave at a paraxial region thereof,
said seventh lens has two aspheric surfaces,
said imaging lens has only seven single lenses with refractive power,
spaces are present between adjacent pairs of the first through seventh lenses, and
said sixth lens has a focal length f6 and said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
0.02< f 7/ f 6<0.3.
2. The imaging lens according to claim 1 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
0.5< f 12/ f< 1.1,
where f is a focal length of a whole lens system.
3. 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:
−1.0< f 2/ f 3<−0.2.
4. The imaging lens according to claim 1 , wherein said first lens and said second lens have a composite focal length f12, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 12/ f 3<−0.1.
5. The imaging lens according to claim 1 , wherein said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−1.5< f 67/ f<− 0.5,
where f is a focal length of a whole lens system.
6. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−3< f 45/ f 67<−0.8.
7. An imaging lens comprising:
a first lens;
a second lens having positive refractive power;
a third lens;
a fourth lens;
a fifth lens;
a sixth lens; and
a seventh lens, arranged in this order from an object side to an image plane side,
wherein said fourth lens is formed in a shape so that a surface thereof on the object side is concave at a paraxial region thereof,
said sixth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof,
said seventh lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof, and
said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
0.5< f 12/ f< 1.1,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 7 , 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:
−1.0< f 2/ f 3<−0.2.
9. The imaging lens according to claim 7 , wherein said first lens and said second lens have a composite focal length f12, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 12/ f 3<−0.1.
10. The imaging lens according to claim 7 , wherein said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−1.5< f 67/ f <−0.5,
where f is a focal length of a whole lens system.
11. The imaging lens according to claim 7 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−3< f 45/ f 67<−0.8.
12. The imaging lens according to claim 7 , wherein said sixth lens has a focal length f6 and said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
0.02< f 7/ f 6<0.3.
13. An imaging lens comprising:
a first lens;
a second lens having positive refractive power;
a third lens;
a fourth lens;
a fifth lens;
a sixth lens; and
a seventh lens, arranged in this order from an object side to an image plane side,
wherein said fourth lens is formed in a shape so that a surface thereof on the object side is concave at a paraxial region thereof,
said sixth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof,
said seventh lens is formed in a meniscus shape at a paraxial region thereof, and
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:
−1.0< f 2/ f 3<−0.2.
14. The imaging lens according to claim 13 , wherein said first lens and said second lens have a composite focal length f12, and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 12/ f 3<−0.1.
15. The imaging lens according to claim 13 , wherein said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−1.5< f 67/ f<− 0.5,
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 13 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−3< f 45/ f 67<−0.8.
17. The imaging lens according to claim 13 , wherein said sixth lens has a focal length f6 and said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
0.02< f 7/ f 6<0.3.