Imaging lens
An imaging lens includes a first lens group having positive refractive power and a second lens group having negative refractive power, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens having positive refractive power, and a third lens having negative refractive power. The second lens group includes a fourth lens having positive refractive power, a fifth lens, and a sixth lens having negative refractive power. The first lens and second lens have specific focal lengths. The first to third lenses have specific Abbe's numbers.
1. An imaging lens comprising:
a first lens group having positive refractive power; and
a second lens group having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens having positive refractive power, a second lens having positive refractive power, and a third lens having negative refractive power,
said second lens group includes a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens having negative refractive power, and
said first lens has a focal length f 1 , said second lens has a focal length f 2 , said fourth lens has a focal length f 4 , said fifth lens has a focal length f 5 , said first lens has an Abbe's number νd 1 , said second lens has an Abbe's number νd 2 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
0.3< f 1/ f 2<0.9,
40<ν d 1<75,
40<ν d 2<75,
15<ν d 3<35,
−15< f 5/ f 4<−5.
2. The imaging lens according to claim 1 , wherein said second lens has the focal length f 2 so that the following conditional expression is satisfied:
1.0< f 2/ f< 2.0,
where f is a focal length of a whole lens system.
3. The imaging lens according to claim 1 , wherein said first lens group has a focal length F 1 , and said second lens group has a focal length F 2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
4. The imaging lens according to claim 1 , wherein said third lens is arranged away from the fourth lens by a distance D 34 on an optical axis so that the following conditional expression is satisfied:
0.05< D 34/ f< 0.35,
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens have a composite focal length f 56 so that the following conditional expression is satisfied:
−3< f 56/ f<− 0.8,
where f is a focal length of a whole lens system.
6. An imaging lens comprising:
a first lens group having positive refractive power; and
a second lens group having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens having positive refractive power, a second lens having positive refractive power, and a third lens having negative refractive power,
said second lens group includes a fourth lens having positive refractive power, a fifth lens, and a sixth lens having negative refractive power, and
said first lens has a focal length f 1 , said second lens has a focal length f 2 , said fifth lens and said sixth lens have a composite focal length f 56 , said first lens has an Abbe's number νd 1 , said second lens has an Abbe's number νd 2 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
0.3< f 1/ f 2<0.9,
40<ν d 1<75,
40<ν d 2<75,
15<ν d 3<35,
−3< f 56/ f<− 0.8,
where f is a focal length of a whole lens system.
7. The imaging lens according to claim 6 , wherein said second lens has the focal length f 2 so that the following conditional expression is satisfied:
1.0< f 2/ f< 2.0.
8. The imaging lens according to claim 6 , wherein said first lens group has a focal length F 1 , and said second lens group has a focal length F 2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
9. The imaging lens according to claim 6 , wherein said third lens is arranged away from the fourth lens by a distance D 34 on an optical axis so that the following conditional expression is satisfied:
0.05< D 34/ f< 0.35.
10. An imaging lens comprising:
a first lens group having positive refractive power; and
a second lens group having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens having positive refractive power, a second lens having positive refractive power, and a third lens having negative refractive power, arranged in this order from the object side to the image plane side,
said second lens group includes a fourth lens having positive refractive power, a fifth lens, and a sixth lens having negative refractive power, and
said first lens has a focal length f 1 , said second lens has a focal length f 2 , said first lens has an Abbe's number νd 1 , said second lens has an Abbe's number νd 2 , and said third lens has an Abbe's number νd 3 so that the following conditional expressions are satisfied:
0.3< f 1/ f 2<0.9,
40<ν d 1<75,
40<ν d 2<75,
15<ν d 3<35.
11. The imaging lens according to claim 10 , wherein said second lens has the focal length f 2 so that the following conditional expression is satisfied:
1.0< f 2/ f< 2.0,
where f is a focal length of a whole lens system.
12. The imaging lens according to claim 10 , wherein said first lens group has a focal length F 1 , and said second lens group has a focal length F 2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
13. The imaging lens according to claim 10 , wherein said third lens is arranged away from the fourth lens by a distance D 34 on an optical axis so that the following conditional expression is satisfied:
0.05< D 34/ f< 0.35,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 10 , wherein said fifth lens has negative refractive power, said fourth lens has a focal length f 4 , and said fifth lens has a focal length f 5 so that the following conditional expression is satisfied:
−15< f 5/ f 4<−5.
15. The imaging lens according to claim 10 , wherein said fifth lens and said sixth lens have a composite focal length f 56 so that the following conditional expression is satisfied:
−3< f 56/ f<− 0.8,
where f is a focal length of a whole lens system.