Imaging lens
A compact low-cost imaging lens which meets the demand for low-profileness, offers high brightness with an F-value of 2.5 or less and a wide field of view, and corrects aberrations properly. Its elements are arranged in order from an object side to an image side: a positive first lens having a convex object-side surface; a negative second lens having a concave image-side surface; a negative third lens; a negative fourth lens as a meniscus double-sided aspheric lens having a convex image-side surface; and a double-sided aspheric fifth lens having a concave image-side surface. The aspheric image-side surface of the fifth lens has a pole-change point off an optical axis, and the imaging lens satisfies conditional expressions (1) and (2): TTL /2 ih ≦0.8 (1) 20<ν d 1−ν d 2<50 (2) where νd1: Abbe number of the first lens at d-ray νd2: Abbe number of the second lens at d-ray ih: maximum image height TTL: total track length.
1. An imaging lens which forms an image of an object on a solid-state image sensor, in which elements are arranged in order from an object side to an image side, comprising:
a first lens with positive refractive power having a convex surface on the object side;
a second lens with negative refractive power having a concave surface on the image side;
a third lens with negative refractive power;
a fourth lens with negative refractive power as a meniscus double-sided aspheric lens having a convex surface on the image side; and
a fifth lens 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) and (2) below are satisfied:
TTL/ 2 ih≦ 0.8 (1)
20<ν d 1−ν d 2<50 (2)
where
νd1: Abbe number of the first lens at d-ray
νd2: Abbe number of the second lens at d-ray
ih: maximum image height
TTL: total track length.
2. The imaging lens according to claim 1 ,
wherein a conditional expression (3) below is satisfied:
0<ν d 3−ν d 4<40 (3)
where
νd3: Abbe number of the third lens at d-ray
νd4: Abbe number of the fourth lens at d-ray.
3. The imaging lens according to claim 1 ,
wherein conditional expressions (4) and (5) below are satisfied:
0.4< f 1/ f< 1.0 (4)
−1.5< f 2345/ f<− 0.6 (5)
where
f: focal length of an overall optical system of the imaging lens
f1: focal length of the first lens
f2345: composite focal length of the second lens, the third lens, the fourth lens, and the fifth lens.
4. The imaging lens according to claim 1 ,
wherein a conditional expression (6) below is satisfied:
1.5< r 4/ f< 2.3 (6)
where
f: focal length of an overall optical system of the imaging lens
r4: curvature radius of the image-side surface of the second lens.
5. The imaging lens according to claim 1 ,
wherein a conditional expression (7) below is satisfied:
−1.9<( r 1+ r 2)/( r 1− r 2)<−0.7 (7)
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.
6. The imaging lens according to claim 1 ,
wherein a conditional expression (8) below is satisfied:
−6.0< f 45/ f<− 3.0 (8)
where
f: focal length of an overall optical system of the imaging lens
f45: composite focal length of the fourth lens and the fifth lens.