Imaging lens
A compact, low-profile, low-cost imaging lens with brightness of F-value 2.5 or less and a wide field of view, which corrects aberrations properly. Elements are arranged from an object side: an aperture stop, positive first lens having a convex object-side surface, negative biconcave second lens having concave object-side and image-side surfaces, positive or negative third lens having a convex object-side surface and at least one aspheric surface; positive meniscus double-sided aspheric fourth lens having a convex image-side surface; and negative double-sided aspheric fifth lens having a concave image-side surface. The fifth lens' aspheric image-side surface has a pole-change point off an optical axis, and the imaging lens satisfies the following conditional expressions: TTL/2 ih ≦0.8 (1) 1.60< Nd 3<1.70 (2) 4.0<| r 9/ r 10|<14.0 (3) where TTL: total track length ih: maximum image height Nd3: third lens refractive index at d-ray r9: curvature radius of the fifth lens object-side surface r10: curvature radius of the fifth lens image-side surface.
1. An imaging lens which forms an image of an object on a solid-state image sensor and provides brightness with an F-value of 2.5 or less, in which elements are arranged in order from an object side to an image side, comprising:
an aperture stop;
a first lens with positive refractive power having a convex surface on the object side;
a second lens with negative refractive power as a biconcave lens having a concave surface on the object side and the image side;
a third lens with positive or negative refractive power having a convex surface on the object side and having at least one aspheric surface;
a fourth lens with positive refractive power as a meniscus double-sided aspheric lens having a convex surface on the image side; and
a fifth lens with negative refractive power as a double-sided aspheric lens having a concave surface on the image side,
wherein the aspheric image-side surface of the fifth lens has a pole-change point off an optical axis, and conditional expressions (1), (2) and (3) below are satisfied:
TTL/2 ih ≦0.8 (1)
1.60< Nd 3<1.70 (2)
4.0<| r 9/ r 10|<14.0 (3)
where
TTL: total track length
ih: maximum image height
Nd3: refractive index of the third lens at d-ray
r9: curvature radius of the object-side surface of the fifth lens
r10: curvature radius of the image-side surface of the fifth lens.
2. The imaging lens according to claim 1 ,
wherein a conditional expression (4) below is satisfied:
3.5<| r 2/ r 1| (4)
where
r1: curvature radius of the object-side surface of the first lens
r2: curvature radius of the image-side surface of the first lens.
3. The imaging lens according to claim 1 ,
wherein a conditional expression (5) below is satisfied:
−1.5< f 2/ f<− 0.5 (5)
where
f: focal length of an overall optical system of the imaging lens
f2: focal length of the second lens.
4. The imaging lens according to claim 1 ,
wherein conditional expressions (6) and (7) below are satisfied:
45<ν d 1<75 (6)
20<ν d 2<35 (7)
where
νd1: Abbe number of the first lens at d-ray
νd2: Abbe number of the second lens at d-ray.
5. The imaging lens according to claim 1 ,
wherein a conditional expression (8) below is satisfied:
0.5< f 1/ f 4<1.8 (8)
where
f1: focal length of the first lens
f4: focal length of the fourth lens.
6. The imaging lens according to claim 1 ,
wherein a conditional expression (9) below is satisfied:
−1.3< r 3/ r 4<−0.7 (9)
where
r3: curvature radius of the object-side surface of the second lens
r4: curvature radius of the image-side surface of the second lens.
7. The imaging lens according to claim 1 ,
wherein a conditional expression (10) below is satisfied:
1.5< r 7/ r 8<3.0 (10)
where
r7: curvature radius of the object-side surface of the fourth lens
r8: curvature radius of the image-side surface of the fourth lens.
8. The imaging lens according to claim 1 ,
wherein conditional expressions (11) and (12) below are satisfied:
45<ν d 4<75 (11)
45<ν d 5<75 (12)
where
νd4: Abbe number of the fourth lens at d-ray
νd5: Abbe number of the fifth lens at d-ray.