Imaging lens
A compact low-cost imaging lens with an F-value of 2.5 or less which achieves both low-profileness and a wide field of view and corrects various aberrations properly. It includes elements arranged from an object side to an image side as follows: a first lens with positive refractive power having a convex object-side surface; a second lens with negative refractive power having a concave object-side surface; a third lens with positive refractive power having convex object-side and image-side surfaces and having at least one aspheric surface; a fourth lens with positive refractive power as a double-sided aspheric lens having a convex image-side surface; and a fifth lens with negative refractive power as a double-sided aspheric lens having a concave image-side surface. The imaging lens satisfies a conditional expression 20<νd 1 −νd 2 <50, where νd 1 denotes Abbe number of the first lens at d-ray, and νd 2 denotes Abbe number of the second lens at d-ray.
1. An imaging lens 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 with positive refractive power having a convex object-side surface;
a second lens with negative refractive power having a concave object-side surface;
a third lens with positive refractive power having a convex object-side surface and a convex image-side surface, at least one of which is aspheric;
a fourth lens with positive refractive power that is a double-sided aspheric lens having a convex image-side surface; and
a fifth lens with negative refractive power that is a double-sided aspheric lens having a concave image-side surface,
wherein a conditional expression (1), (5), and (6′) below are satisfied:
20<ν d 1−ν d 2<50 (1)
0.8< f 1/ f 4<1.4 (5)
−1.2< f 5/ f≦− 0.83 (6′)
where
νd 1 : Abbe number of the first lens at d-ray,
νd 2 : Abbe number of the second lens at d-ray,
f: overall focal length of the imaging lens,
f1: focal length of the first lens,
f4: focal length of the fourth lens, and
f5: focal length of the fifth lens.
2. The imaging lens according to claim 1 , wherein conditional expressions (2) and (3) below are satisfied:
0.5< f 1/| f 2|<1.2 (2)
0.04< T 12/ f< 0.14 (3)
where
f2: focal length of the second lens, and
T 12 : air gap between the first lens and the second lens on an optical axis of the imaging lens.
3. The imaging lens according to claim 2 , wherein a conditional expression (4) below is satisfied:
2.0< f 3/ f< 8.0 (4)
where
f3: focal length of the third lens.
4. The imaging lens according to claim 2 , wherein a conditional expression (7) below is satisfied:
−0.4<( r 1+ r 2)/( r 1− r 2)<0.15 (7)
where
r 1 : curvature radius of the object-side surface of the first lens, and
r 2 : curvature radius of an image-side surface of the first lens.
5. The imaging lens according to claim 4 , wherein a conditional expression (8) below is satisfied:
−1.9<( r 3+ r 4)/( r 3− r 4)<−0.9 (8)
where
r 3 : curvature radius of the object-side surface of the second lens, and
r 4 : curvature radius of an image-side surface of the second lens.
6. The imaging lens according to claim 5 , wherein a conditional expression (9) below is satisfied:
−1.0<( r 5+ r 6)/( r 5− r 6)<1.0 (9)
where
r 5 : curvature radius of the object-side surface of the third lens, and
r 6 : curvature radius of the image-side surface of the third lens.
7. The imaging lens according to claim 1 , wherein a conditional expression (4) below is satisfied:
2.0< f 3/ f< 8.0 (4)
where
f3: focal length of the third lens.
8. The imaging lens according to claim 1 , wherein a conditional expression (7) below is satisfied:
−0.4<( r 1+ r 2)/( r 1− r 2)<0.15 (7)
where
r 1 : curvature radius of the object-side surface of the first lens, and
r 2 : curvature radius of an image-side surface of the first lens.
9. The imaging lens according to claim 8 , wherein a conditional expression (8) below is satisfied:
−1.9<( r 3+ r 4)/( r 3− r 4)<−0.9 (8)
where
r 3 : curvature radius of the object-side surface of the second lens, and
r 4 : curvature radius of an image-side surface of the second lens.
10. The imaging lens according to claim 9 , wherein a conditional expression (9) below is satisfied:
−1.0<( r 5+ r 6)/( r 5− r 6)<1.0 (9)
where
r 5 : curvature radius of the object-side surface of the third lens, and
r 6 : curvature radius of the image-side surface of the third lens.
11. The imaging lens according to claim 1 , wherein a conditional expression (8) below is satisfied:
−1.9<( r 3+ r 4)/( r 3− r 4)<−0.9 (8)
where
r 3 : curvature radius of the object-side surface of the second lens, and
r 4 : curvature radius of an image-side surface of the second lens.
12. The imaging lens according to claim 11 , wherein a conditional expression (9) below is satisfied:
−1.0<( r 5+ r 6)/( r 5− r 6)<1.0 (9)
where
r 5 : curvature radius of the object-side surface of the third lens, and
r 6 : curvature radius of the image-side surface of the third lens.
13. The imaging lens according to claim 1 , wherein a conditional expression (9) below is satisfied:
−1.0<( r 5+ r 6)/( r 5− r 6)<1.0 (9)
where
r 5 : curvature radius of the object-side surface of the third lens, and
r 6 : curvature radius of the image-side surface of the third lens.
14. An imaging lens 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 with positive refractive power having a convex object-side surface;
a second lens with negative refractive power having a concave object-side surface;
a third lens with positive refractive power having a convex object-side surface and a convex image-side surface, at least one of which is aspheric;
a fourth lens with positive refractive power that is a double-sided aspheric lens having a convex image-side surface; and
a fifth lens with negative refractive power that is a double-sided aspheric lens having a concave image-side surface,
wherein conditional expressions (1), (2′), (3′), and (4′) below are satisfied:
20<ν d 1−ν d 2<50 (1)
0.5 <f 1/| f 2|≦0.76 (2′)
0.08≦ T 12/ f< 0.14 (3′)
3.57≦ f 3/ f< 8.0 (4′)
where
νd 1 : Abbe number of the first lens at d-ray,
νd 2 : Abbe number of the second lens at d-ray,
f: overall focal length of the imaging lens,
f1: focal length of the first lens,
f2: focal length of the second lens,
f3: focal length of the third lens, and
T 12 : air gap between the first lens and the second lens on an optical axis of the imaging lens.