Imaging lens

1. An imaging lens comprising:

a first lens having positive refractive power;

a second lens having positive refractive power;

a third lens having negative refractive power;

a fourth lens having positive refractive power;

a fifth lens;

a sixth lens;

a seventh lens;

an eighth lens; and

a ninth lens having negative refractive power, arranged in this order from an object side to an image plane side,

wherein said ninth lens is formed in a shape so that a surface thereof on the image plane side has an aspherical shape having an inflection point, and

said eighth lens is a meniscus lens having a convex object-side surface near an optical axis.

2. The imaging lens according to claim 1 , wherein said seventh lens has a thickness T7 on an optical axis thereof and said eighth lens has a thickness T8 on an optical axis thereof so that the following conditional expression is satisfied:

0.5< T 8/ T 7<3.

3. The imaging lens according to claim 1 , wherein said eighth lens is disposed away from the ninth lens by a distance D89 on an optical axis thereof so that the following conditional expression is satisfied:

0.02< D 89/ f< 0.15,

where f is a focal length of a whole lens system.

4. The imaging lens according to claim 1 , wherein said ninth lens is formed in the shape so that the surface thereof on the image plane side has a paraxial curvature radius R9r so that the following conditional expression is satisfied:

0.2< R 9 r/f< 0.6,

where f is a focal length of a whole lens system.

5. The imaging lens according to claim 1 , wherein said ninth lens has a focal length f9 so that the following conditional expression is satisfied:

−3.5< f 9/ f<− 0.2,

where f is a focal length of a whole lens system.