Imaging lens
An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power, arranged in this order from an object side to an image plane side. Further, the first lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive. The second lens is formed in a shape so that a curvature radius of a surface thereof on the object side is negative and a curvature radius of a surface thereof on the image plane side is positive. The third lens is formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are both positive.
1. An imaging lens comprising:
a first lens having positive refractive power, said first lens being formed in a shape so that a curvature radius of a surface thereof on an object side is positive;
a second lens having negative refractive power, said second lens being formed in a shape so that a curvature radius of a surface thereof on the object side is negative and a curvature radius of a surface thereof on an image plane side is positive; and
a third lens having positive refractive power, said third lens being formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are both positive, arranged in this order from the object side to the image plane side,
wherein said first lens is arranged so that the surface thereof on the image plane side is away from the surface of the second lens on the object side by a distance T 1 on an optical axis, and
said second lens is arranged so that the surface thereof on the image plane side is away from the surface of the third lens on the object side by a distance T 2 on the optical axis so that the following conditional expression is satisfied:
1.6≦ T 1/ T 2<2.0
said first lens and said second lens have a composite focal length f 12 so that the following conditional expression is satisfied:
4.0< f 12/ f< 10.0
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said second lens has a surface on the image plane side having a curvature radius R 2 r and said third lens has a surface on the object side having a curvature radius R 3 f so that the following conditional expression is satisfied:
2.0< R 2 r/R 3 f< 35.0.
3. The imaging lens according to claim 1 , wherein said second lens has a surface on the image plane side having a curvature radius R 2 r so that the following conditional expression is satisfied:
0.6 <R 2 r/f< 10.0.