Imaging lens
An imaging lens includes a first lens having negative refractive power; an aperture stop; a second lens; a third lens; a fourth lens; a fifth lens; and a sixth lens, arranged in this order from an object side to an image plane side. The fourth lens is formed in a meniscus shape at a paraxial region thereof. The fifth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof. The sixth lens is formed in a meniscus shape at a paraxial region thereof. The first lens and the sixth lens have specific Abbe's numbers.
1. An imaging lens comprising:
a first lens having negative refractive power;
an aperture stop;
a second lens;
a third lens;
a fourth lens;
a fifth lens; and
a sixth lens, arranged in this order from an object side to an image plane side,
wherein said fourth lens is formed in a meniscus shape at a paraxial region thereof,
said fifth lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof,
said sixth lens is formed in a meniscus shape at a paraxial region thereof, and
said first lens has an Abbe's number ν1, said sixth lens has an Abbe's number ν6, and said
second lens and said third lens have a composite focal length f23 so that the following conditional expressions are satisfied:
40<ν1<75,
10<ν6<40,
0.2 <f 23 /f <1,
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said first lens is disposed away from the second lens by a distance D12 on an optical axis thereof so that the following conditional expression is satisfied:
0.05< D 12 /f <0.8,
where f is a focal length of a whole lens system.
3. The imaging lens according to claim 1 , wherein said second lens is disposed away from the third lens by a distance D23 on an optical axis thereof so that the following conditional expression is satisfied:
0.001< D 23 /f< 0.3,
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said first lens is disposed away from the second lens by a distance D12 on an optical axis thereof, and said second lens is disposed away from the third lens by a distance D23 on an optical axis thereof so that the following conditional expression is satisfied:
2< D 12 /D 23<30.
5. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−5< f 6 /f< −0.5,
where f is a focal length of a whole lens system.
6. The imaging lens according to claim 1 , wherein said fifth lens has a thickness T5 on an optical axis thereof and said sixth lens has a thickness T6 on an optical axis thereof so that the following conditional expression is satisfied:
0.5< T 5 /T 6<3.5.
7. An imaging lens comprising:
a first lens having negative refractive power;
an aperture stop;
a second lens;
a third lens;
a fourth lens;
a fifth lens; and
a sixth lens, arranged in this order from an object side to an image plane side,
wherein said second lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are convex at a paraxial region thereof,
said third lens is formed in a shape so that a surface thereof on the object side is convex at a paraxial region thereof,
said fourth lens is formed in a meniscus shape at a paraxial region thereof,
said fifth 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 is disposed away from the second lens by a distance D12 on an optical axis thereof,
and said fifth lens has a thickness T5 on an optical axis thereof, said sixth lens has a thickness T6 on an optical axis thereof, and said second lens and said third lens have a composite focal length f23 so that the following conditional expressions are satisfied:
0.05< D 12 /f <0.8,
0.5< T 5/ T 6<3.5,
0.2< f 23 /f <1,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 7 , wherein said second lens is disposed away from the third lens by a distance D23 on an optical axis thereof so that the following conditional expression is satisfied:
0.001< D 23 /f< 0.3.
9. The imaging lens according to claim 7 , wherein said second lens is disposed away from the third lens by a distance D23 on an optical axis thereof so that the following conditional expression is satisfied:
2< D 12 /D 23<30.
10. The imaging lens according to claim 7 , wherein said sixth lens has a focal length f 6 so that the following conditional expression is satisfied:
−5< f 6/ f< −0.5.
11. The imaging lens according to claim 7 , wherein said sixth lens has an Abbe's number ν6 so that the following conditional expression is satisfied:
10<ν6<40.