Imaging lens
An imaging lens includes a first lens having positive refractive power; a second lens having negative 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. The lenses are arranged in this order from an object side to an image plane side. The 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.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative 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 second lens has a focal length f2 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.1 <f 2 /f 3<1.2.
2. The imaging lens according to claim 1 , wherein said eighth lens is disposed away from the ninth lens by a distance D 89 so that the following conditional expression is satisfied:
0.05< D 89 /f< 0.15,
where f is a focal length of a whole lens system.
3. 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.
4. The imaging lens according to claim 1 , wherein said ninth lens has a focal length f9 so that the following conditional expression is satisfied:
−2< f 9 /f< −0.2,
where f is a focal length of a whole lens system.
5. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative 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 disposed away from the ninth lens by a distance D89 so that the following conditional expression is satisfied:
0.05 <D 89 /f< 0.15,
where f is a focal length of a whole lens system.
6. The imaging lens according to claim 5 , 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:
0.1< f 2 /f 3<1.2.
7. The imaging lens according to claim 5 , 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 the focal length of the whole lens system.
8. The imaging lens according to claim 5 , wherein said ninth lens has a focal length f9 so that the following conditional expression is satisfied:
−2 <f 9/ f< −0.2,
where f is a focal length of the whole lens system.