Imaging lens
An imaging lens in which a positive first lens group, a positive second lens group, and a negative third lens group are arranged in order from the object side. The first lens group includes a positive first lens having a convex object-side surface and a second lens. The second lens group includes third and fourth lenses each having at least one aspheric surface. The third lens group includes a fifth lens, a sixth lens as a double-sided aspheric lens, and a seventh lens having a concave image-side surface near an optical axis. The lenses are not joined to each other, the seventh lens has an aspheric image-side surface whose shape changes from concave to convex as the distance from the optical axis increases, and an F-number is less than 1.8.
1. An imaging lens with a fixed focal length which forms an image of an object on a solid-state image sensor, in which lenses are arranged in order from an object side to an image side of the imaging lens, comprising:
a first lens group with positive refractive power,
the first lens group including, in order from the object side: a first lens with positive refractive power having a convex object-side surface, and a second lens;
a second lens group with positive refractive power, the second lens group including, in order from the object side: a third lens, and a fourth lens, each having at least one aspheric surface; and
a third lens group with negative refractive power, the third lens group including, in order from the object side: a fifth lens, a sixth lens that is a double-sided aspheric lens, and a seventh lens having a concave image-side surface near an optical axis of the imaging lens,
wherein the lenses are not joined to each other, the image-side surface of the seventh lens has an aspheric surface whose shape changes from concave to convex as a distance from the optical axis increases, and an F-number is less than 1.8.
2. The imaging lens according to claim 1 , wherein the second lens has negative refractive power and a concave image-side surface near the optical axis.
3. The imaging lens according to claim 1 , wherein the fifth lens has negative refractive power and a concave object-side surface near the optical axis.
4. The imaging lens according to claim 1 , wherein the sixth lens has positive refractive power and a convex image-side surface near the optical axis, and the seventh lens has negative refractive power.
5. The imaging lens according to claim 1 , wherein conditional expressions (1) and (2) given below are satisfied:
45<ν d 1<70 (1)
20<ν d 2<35 (2)
where
νd1: Abbe number of the first lens at d-ray, and
νd2: Abbe number of the second lens at d-ray.
6. The imaging lens according to claim 1 , wherein conditional expressions (4) and (5) given below are satisfied:
20<ν d 5<35 (4)
45<ν d 6<70 (5)
where
νd5: Abbe number of the fifth lens at d-ray, and
νd6: Abbe number of the sixth lens at d-ray.
7. The imaging lens according to claim 1 , wherein conditional expressions (7) and (8) given below are satisfied:
0.62< f 1/ f< 1.01 (7)
−2.58< f 2/ f<− 0.87 (8)
where
f: overall focal length of the imaging lens,
f1: focal length of the first lens, and
f2: focal length of the second lens.
8. The imaging lens according to claim 1 , wherein a conditional expression (9) given below is satisfied:
0.96< f 12/ f< 2.07 (9)
where
f: overall focal length of the imaging lens, and
f12: composite focal length of the first lens group.
9. The imaging lens according to claim 1 , wherein a conditional expression (10) given below is satisfied:
0.65< f 12/ f 34<1.67 (10)
where
f12: composite focal length of the first lens group, and
f34: composite focal length of the second lens group.
10. The imaging lens according to claim 1 , wherein a conditional expression (11) given below is satisfied:
−2.37< f 567/ f<− 0.55 (11)
where
f: overall focal length of the imaging lens, and
f567: composite focal length of the third lens group.
11. An imaging lens consisting of seven lens elements in three lens groups with a fixed focal length which forms an image of an object on a solid-state image sensor, in which lenses are arranged in order from an object side to an image side of the imaging lens, comprising:
a first lens group including two lens elements,
the first lens group including, in order from the object side: a first lens with positive refractive power having a convex object-side surface, and a second lens;
a second lens group including two lens elements, the second lens group including, in order from the object side: a third lens, and a fourth lens, each having at least one aspheric surface; and
a third lens group including three lens elements, the third lens group including, in order from the object side: a fifth lens, a sixth lens that is a double-sided aspheric lens, and a seventh lens having a concave image-side surface near an optical axis of the imaging lens,
wherein the lenses are not joined to each other, the image-side surface of the seventh lens has an aspheric surface whose shape changes from concave to convex as a distance from the optical axis increases, and conditional expressions (7) and (8b) given below are satisfied:
0.62< f 1/ f< 1.01 (7)
−1.482≦ f 2/ f<− 0.87 (8b)
where
f: overall focal length of the imaging lens,
f1: focal length of the first lens, and
f2: focal length of the second lens.
12. The imaging lens according to claim 11 , wherein the second lens has negative refractive power and a concave image-side surface near the optical axis.
13. The imaging lens according to claim 11 , wherein the fifth lens has negative refractive power and a concave object-side surface near the optical axis.
14. The imaging lens according to claim 11 , wherein the sixth lens has positive refractive power and a convex image-side surface near the optical axis, and the seventh lens has negative refractive power.
15. The imaging lens according to claim 11 , wherein conditional expressions (1) and (2) given below are satisfied:
45<ν d 1<70 (1)
20<ν d 2<35 (2)
where
νd1: Abbe number of the first lens at d-ray, and
νd2: Abbe number of the second lens at d-ray.
16. The imaging lens according to claim 11 , wherein conditional expressions (4) and (5) given below are satisfied:
20<ν d 5<35 (4)
45<ν d 6<70 (5)
where
νd5: Abbe number of the fifth lens at d-ray, and
νd6: Abbe number of the sixth lens at d-ray.
17. The imaging lens according to claim 11 , wherein a conditional expression 9 given below is satisfied:
0.96< f 12/ f< 2.07 (9)
where
f12: composite focal length of the first lens group.
18. The imaging lens according to claim 11 , wherein a conditional expression (10) given below is satisfied:
0.65< f 12/ f 34<1.67 (10)
where
f12: composite focal length of the first lens group, and
f34: composite focal length of the second lens group.
19. The imaging lens according to claim 11 , wherein a conditional expression (11) given below is satisfied:
−2.37< f 567/ f<− 0.55 (11)
where
f567: composite focal length of the third lens group.
20. The imaging lens according to claim 11 , wherein an F-number is less than 2.0.