Imaging lens
An imaging lens includes a first lens having negative refractive power; a second lens; a third lens; a fourth lens having positive refractive power; and a fifth lens. The second lens has a surface on the object side formed in an aspheric shape. The first to fifth lenses are formed of materials having specific Abbe's numbers to satisfy specific conditions.
1. An imaging lens comprising:
a first lens having negative refractive power;
a second lens;
a third lens;
a fourth lens; and
a fifth lens, arranged in this order from an object side to an image plane side,
wherein said second lens has a surface on the object side formed into an aspheric shape,
said first lens, said second lens, said third lens, and said fourth lens are formed of a material having an Abbe's number between 45 and 75,
said fifth lens is formed of a material having an Abbe's number between 20 and 40, and
said first lens has a focal length f1 so that the following conditional expression is satisfied:
−3.5< f 1/ f<− 1.5
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−1.5< f 5/ f<− 0.5.
3. The imaging lens according to claim 1 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 1/ f 2<1.5.
4. The imaging lens according to claim 1 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 2.5.
5. The imaging lens according to claim 1 , wherein said second lens is situated away from the third lens by a distance dA on an optical axis thereof so that the following conditional expression is satisfied:
0.5< dA/f< 1.0.
6. An imaging lens comprising:
a first lens having negative refractive power;
a second lens having negative refractive power;
a third lens;
a fourth lens; and
a fifth lens, arranged in this order from an object side to an image plane side,
wherein said second lens has a surface on the object side formed into an aspheric shape,
said fifth lens has a surface on the image plane side having a negative curvature radius, and
said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−1.5< f 5/ f<− 0.5
where f is a focal length of a whole lens system.
7. The imaging lens according to claim 6 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 1/ f 2<1.5.
8. The imaging lens according to claim 6 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 2.5.
9. The imaging lens according to claim 6 , wherein said second lens is situated away from the third lens by a distance dA on an optical axis thereof so that the following conditional expression is satisfied:
0.5< dA/f< 1.0.
10. An imaging lens comprising:
a first lens having negative refractive power;
a second lens;
a third lens;
a fourth lens; and
a fifth lens, arranged in this order from an object side to an image plane side,
wherein said second lens has a surface on the object side formed into an aspheric shape, and
said third lens has a focal length f3, said fifth lens has a focal length f5, and said second lens is situated away from the third lens by a distance dA on an optical axis thereof so that the following conditional expressions are satisfied:
0.5< f 3/ f< 2.5
−1.5< f 5/ f<− 0.5
0.5< dA/f< 1.0
where f is a focal length of a whole lens system.
11. The imaging lens according to claim 10 , wherein said second lens has negative refractive power.
12. The imaging lens according to claim 10 , wherein said first lens has a focal length f1 so that the following conditional expression is satisfied:
−3.5< f 1/ f<− 1.5.
13. The imaging lens according to claim 10 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 1/ f 2<1.5.
14. An imaging lens comprising:
a first lens having negative refractive power;
a second lens;
a third lens;
a fourth lens; and
a fifth lens, arranged in this order from an object side to an image plane side,
wherein said second lens has a surface on the object side formed into an aspheric shape,
said first lens, said second lens, said third lens, and said fourth lens are formed of a material having an Abbe's number between 45 and 75,
said fifth lens is formed of a material having an Abbe's number between 20 and 40,
said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 2.5
where f is a focal length of a whole lens system.
15. The imaging lens according to claim 14 , wherein said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−1.5< f 5/ f<− 0.5.
16. The imaging lens according to claim 14 , wherein said first lens has a focal length f1 so that the following conditional expression is satisfied:
−3.5< f 1/ f<− 1.5.
17. The imaging lens according to claim 14 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 1/ f 2<1.5.
18. The imaging lens according to claim 14 , wherein said second lens is situated away from the third lens by a distance dA on an optical axis thereof so that the following conditional expression is satisfied:
0.5< dA/f< 1.0.