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, comprising, in order from an object side to an image side of the imaging lens: a first lens group including, in order from the object side, a first lens having positive refractive power, and a second lens having negative refractive power; a second lens group including, in order from the object side, a third lens having at least one aspheric surface and a convex surface facing the object side near the optical axis, and a fourth lens having at least one aspheric surface; and a third lens group having negative composite refractive power and 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 surface facing the image side near the optical axis, wherein: an 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 when f is an overall focal length of the imaging lens, f2 is a focal length of the second lens and f567 is a composite focal length of the third lens group, conditional expressions (8b) and (11) given below are satisfied:
−1.482< f 2/ f<− 0.87 (8b)
−2.37< f 567/ f<− 0.55 (11),
wherein the imaging lens has a total of seven lenses.
2. The imaging lens according to claim 1 ,
wherein when νd1 is an Abbe number of the first lens at d-ray, and
νd2 is an Abbe number of the second lens at d-ray,
conditional expressions (1) and (2) given below are satisfied:
45< νd 1<70 (1)
20<ν d 2<35 (2).
3. The imaging lens according to claim 1 ,
wherein when νd5 is an Abbe number of the fifth lens at d-ray, and
νd6 is an Abbe number of the sixth lens at d-ray,
conditional expressions (4) and (5) given below are satisfied:
20<ν d 5<35 (4)
45<ν d 6<70 (5).
4. The imaging lens according to claim 1 ,
wherein when f is an overall focal length of the imaging lens,
f1 is a focal length of the first lens, and
f2 is a focal length of the second lens,
a conditional expression (7) given below is satisfied:
0.62< f 1/ f< 1.01 (7).
5. The imaging lens according to claim 1 ,
wherein when f is an overall focal length of the imaging lens, and
f12 is a composite focal length of the first lens group,
a conditional expression (9) given below is satisfied:
0.96< f 12/ f< 2.07 (9).
6. The imaging lens according to claim 1 ,
wherein when f12 is a composite focal length of the first lens group, and
f34 is a composite focal length of the second lens group,
a conditional expression (10) given below is satisfied:
0.65< f 12/ f 34<1.67 (10).
7. The imaging lens according to claim 1 ,
wherein the first lens having a convex surface facing the object side,
the second lens having a concave surface facing the image side near the optical axis,
the fifth lens having negative refractive power and a concave surface facing the object
side near the optical axis,
the sixth lens having positive refractive power and a convex surface facing the image side near the optical axis; and
the seventh lens having negative refractive power.
8. An imaging lens with a fixed focal length which forms an image of an object on a solid-state image sensor, comprising, in order from an object side to an image side of the imaging lens: a first lens group having a positive composite refractive power and including, in order from the object side, a first lens having positive refractive power, and a second lens; a second lens group including, in order from the object side, a third lens having at least one aspheric surface and a convex surface facing the object side near the optical axis, and a fourth lens having at least one aspheric surface and a convex surface facing the image side surface near the optical axis; and a 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 surface facing the image side near the optical axis, wherein: an 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 wherein an F-number of the imaging lens is less than 1.8, when f is an overall focal length of the imaging lens, f2 is a focal length of the second lens, and f12 is a composite focal length of the first lens group, conditional expressions (8b) and (9) given below are satisfied:
−1.482≤ f 2/ f<− 0.87 (8b)
0.96< f 12/ f< 2.07 (9),
wherein the imaging lens has a total of seven lenses.
9. The imaging lens according to claim 8 ,
wherein when νd1 is an Abbe number of the first lens at d-ray, and
vd 2 is an Abbe number of the second lens at d-ray,
conditional expressions (1) and (2) given below are satisfied:
45<ν d 1<70 (1)
20<ν d 2<35 (2).
10. The imaging lens according to claim 8 ,
wherein when νd5 is an Abbe number of the fifth lens at d-ray, and
νd6 is an Abbe number of the sixth lens at d-ray,
conditional expressions (4) and (5) given below are satisfied:
20<ν d 5<35 (4)
45<ν d 6<70 (5).
11. The imaging lens according to claim 8 ,
wherein when f is an overall focal length of the imaging lens,
f1 is a focal length of the first lens, and
f2 is a focal length of the second lens,
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).
12. The imaging lens according to claim 8 ,
wherein when f12 is a composite focal length of the first lens group, and
f34 is a composite focal length of the second lens group,
a conditional expression (10) given below is satisfied:
0.65< f 12/ f 34<1.67 (10).
13. The imaging lens according to claim 8 ,
wherein the first lens having a convex surface facing the object side,
the second lens having negative refractive power and a concave surface facing the image side near the optical axis,
the fifth lens having negative refractive power and a concave surface facing the object side near the optical axis,
the sixth lens having positive refractive power and a convex surface facing the image side near the optical axis; and
the seventh lens having negative refractive power.
14. An imaging lens with a fixed focal length which forms an image of an object on a solid-state image sensor, comprising, in order from an object side to an image side of the imaging lens: a first lens group having a positive composite refractive power and including, in order from the object side, a first lens having positive refractive power, and a second lens; a second lens group having a positive composite refractive power and including, in order from the object side, a third lens having at least one aspheric, and a fourth lens having at least one aspheric surface; a third lens group having a negative composite refractive power and 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 surface facing the image side near the optical axis, wherein: an 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 wherein when f is an overall focal length of the imaging lens, f2 is a focal length of the second lens, f12 is a composite focal length of the first lens group, f34 is a composite focal length of the second lens group, and f567 is a composite focal length of the third lens group, conditional expressions (8b), (9), (10), and (11a) given below are satisfied:
−1.482≤ f 2/ f<− 0.87 (8b)
0.96< f 12/ f< 2.07 (9)
0.65< f 12/ f 34<1.67 (10)
−2.18< f 567/ f<− 0.62 (11a),
wherein the imaging lens has a total of seven lenses.
15. The imaging lens according to claim 14 ,
wherein when νd1 is an Abbe number of the first lens at d-ray, and
vd 2 is an Abbe number of the second lens at d-ray,
conditional expressions (1) and (2) given below are satisfied:
45<ν d 1<70 (1)
20<ν d 2<35 (2).
16. The imaging lens according to claim 14 ,
wherein when νd5 is an Abbe number of the fifth lens at d-ray, and
νd6 is an Abbe number of the sixth lens at d-ray,
conditional expressions (4) and (5) given below are satisfied:
20<ν d 5<35 (4)
45<ν d 6<70 (5).
17. The imaging lens according to claim 14 ,
wherein when f is an overall focal length of the imaging lens,
f1 is a focal length of the first lens, and
f2 is a focal length of the second lens,
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).
18. The imaging lens according to claim 14 ,
wherein the first lens having a convex surface facing the object side,
the second lens having negative refractive power and a concave surface facing the image side near the optical axis,
the fifth lens having negative refractive power and a concave surface facing the object side near the optical axis,
the sixth lens having positive refractive power and a convex surface facing the image side near the optical axis; and
the seventh lens having negative refractive power.