Imaging lens
An imaging lens includes a first lens group and a second lens group 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 negative refractive power, and a third lens, arranged with a space in between. The second lens group includes a front side lens group having negative refractive power and a rear side lens group having positive refractive power. The front side lens group includes a fourth lens and a fifth lens arranged with a space in between. The rear side lens group includes a sixth lens and a seventh lens arranged with a space in between. The fourth lens is formed in a shape so that a surface thereof on the object side has a specific curvature radius so that a specific conditional expression is satisfied.
1. An imaging lens comprising:
a first lens group; and
a second lens group, 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 negative refractive power, and a third lens, arranged with a space in between,
said second lens group includes a front side lens group having negative refractive power and a rear side lens group having positive refractive power,
said front side lens group includes a fourth lens and a fifth lens arranged with a space in between,
said rear side lens group includes a sixth lens and a seventh lens arranged with a space in between, and
said fourth lens is formed in a shape so that a surface thereof on the object side has a curvature radius R4f so that the following conditional expression is satisfied:
−0.6< R 4 f/f<− 0.1,
where f is a focal length of a whole lens system.
2. The imaging lens according to claim 1 , wherein said first lens group is arranged to be away from the second lens group by a distance Da on an optical axis thereof so that the following conditional expression is satisfied:
0.05< Da/f< 0.3.
3. The imaging lens according to claim 1 , wherein said front side lens group is arranged to be away from the rear side lens group by a distance Db on an optical axis thereof so that the following conditional expression is satisfied:
0.02< Db/f< 0.1.
4. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−3< f 4/ f<− 1.
5. The imaging lens according to claim 1 , wherein said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
3<| f 5|/ f< 60.
6. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−1.3< f 4/ f 6<−0.6.
7. An imaging lens comprising:
a first lens group; and
a second lens group, 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, and a third lens, arranged with a space in between,
said second lens group includes a front side lens group and a rear side lens group having positive refractive power,
said front side lens group includes a fourth lens having negative refractive power and a fifth lens having positive refractive power arranged with a space in between,
said rear side lens group includes a sixth lens and a seventh lens arranged with a space in between, and
said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
3<| f 5|/ f< 60,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 7 , wherein said first lens group is arranged to be away from the second lens group by a distance Da on an optical axis thereof so that the following conditional expression is satisfied:
0.05< Da/f< 0.3.
9. The imaging lens according to claim 7 , wherein said fourth lens is formed in a shape so that a surface thereof on the object side has a curvature radius R4f so that the following conditional expression is satisfied:
−0.6< R 4 f/f<− 0.1.
10. The imaging lens according to claim 7 , wherein said front side lens group is arranged to be away from the rear side lens group by a distance Db on an optical axis thereof so that the following conditional expression is satisfied:
0.02< Db/f< 0.1.
11. The imaging lens according to claim 7 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−3< f 4/ f<− 1.
12. The imaging lens according to claim 7 , wherein said fourth lens has a focal length f4 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−1.3< f 4/ f 6<−0.6.
13. An imaging lens comprising:
a first lens group; and
a second lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens, a second lens, and a third lens, arranged with a space in between,
said first lens group further includes an aperture stop disposed between the first lens and the second lens,
said second lens group includes a front side lens group and a rear side lens group,
said front side lens group includes a fourth lens having negative refractive power and a fifth lens having positive refractive power arranged with a space in between,
said rear side lens group includes a sixth lens having positive refractive power and a seventh lens arranged with a space in between,
each of said first lens, said second lens, said third lens, said fourth lens, said fifth lens, said sixth lens, and said seventh lens is formed of a plastic,
said fifth lens is formed in a meniscus shape so that a surface thereof facing the object side is convex near an optical axis thereof, and
said first lens group is arranged to be away from the second lens group by a distance Da on an optical axis thereof so that the following conditional expression is satisfied:
0.05 <Da/f< 0.3,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 13 , wherein said fourth lens is formed in a shape so that a surface thereof on the object side has a curvature radius R4f so that the following conditional expression is satisfied:
−0.6< R 4 f/f<− 0.1.
15. The imaging lens according to claim 13 , wherein said seventh lens is formed in a shape so that a surface thereof on the image plane side has a curvature radius R7r so that the following conditional expression is satisfied:
0.2< R 7 r/f< 0.6.
16. The imaging lens according to claim 13 , wherein said front side lens group is arranged to be away from the rear side lens group by a distance Db on an optical axis thereof so that the following conditional expression is satisfied:
0.02< Db/f< 0.1.
17. The imaging lens according to claim 13 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−3< f 4/ f<− 1.
18. The imaging lens according to claim 13 , wherein said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
3<| f 5|/ f< 60.
19. The imaging lens according to claim 13 , wherein said fourth lens has a focal length f4 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−1.3< f 4/ f 6<−0.6.