Imaging lens
An imaging lens includes a first lens; a second lens; a third lens having positive refractive power; a fourth lens; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side. The second lens has a convex surface facing the object side near an optical axis thereof. The sixth lens has a convex surface facing the image plane side near an optical axis thereof. The first lens is arranged so that a surface thereof on the object side is away from an image plane by a specific distance on an optical axis thereof. The second lens is arranged to be away from the third lens by a specific distance on the optical axis thereof. The fourth lens is arranged to be away from the fifth lens by a specific distance on an optical axis thereof.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens having positive refractive power;
a fourth lens;
a fifth lens; and
a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said second lens has a convex surface facing the object side at a paraxial region thereof,
said third lens has a convex surface facing the image plane side at a paraxial region thereof,
said sixth lens has a convex surface facing the image plane side at a paraxial region thereof, and
said first lens is arranged so that a surface thereof on the object side is away from an image plane by a distance La on an optical axis thereof, and said fourth lens is arranged to be away from the fifth lens by a distance D45 on an optical axis thereof so that the following conditional expressions are satisfied:
1.2< La/H max <1.8,
0.04< D 45/ f< 0.5,
where f is a focal length of a whole lens system, and Hmax is a maximum image height of the image plane.
2. The imaging lens according to claim 1 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
1< f 3/ f< 5.
3. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−2.0< f 56/ f<− 0.1.
4. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.0< f 6/ f<− 0.5.
5. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
0.5< f 4/ f< 5.0.
6. The imaging lens according to claim 1 , wherein said third lens has a focal length f3 and said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
0.5< f 3/ f 4<4.5.
7. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expression is satisfied:
2< f 45/ f< 8.