Imaging lens
An imaging lens forms an image on a solid-state image sensor. The constituent elements are arranged in order from an object side: an aperture stop, positive first lens having a convex object-side surface, negative second lens having a concave image-side surface, positive or negative double-sided aspheric third lens, positive fourth lens having a convex image-side surface, and negative double-sided aspheric fifth lens having a concave image-side surface. In addition, all of the lenses are made of plastic, and conditional expressions (1) through (4) below are satisfied: 2.0< r 7/ r 8<5.0; (1) −1.35< f 4/ f 5<−0.8; (2) TLA /2 ih <0.80; (3) 1.50< Nd <1.65, (4) where r7 denotes curvature radius of the fourth lens object-side surface, r8 denotes curvature radius of the fourth lens image-side surface, f4 denotes fourth lens focal length, f5 denotes fifth lens focal length, TLA denotes total track length, ih denotes maximum image height, and Nd denotes refractive index at d-ray of the first to fifth lenses.
1. An imaging lens to form an image of an object on a solid-state image sensor, in which the 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 having a concave surface on the image side, a third lens with positive or negative refractive power having an aspheric shape on both lens surfaces, a fourth lens with positive refractive power having a convex surface on the image side, and a fifth lens with negative refractive power having a concave surface on the image side near an optical axis as a double-sided aspheric lens, all the lenses are made of plastic material, and
conditional expressions (1) through (4) below are satisfied:
2.928< r 7/ r 8<5.0 (1)
−1.128< f 4/ f 5<−1.032 (2)
TLA/ 2 ih≦ 0.747 (3)
1.50< Nd< 1.65 (4)
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
f4: focal length of the fourth lens
f5: focal length of the fifth lens
TLA: distance on the optical axis from the object-side surface of an optical element nearest to the object to the image plane in which filters are removed
ih: maximum image height
Nd: refractive index with respect to d-ray of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens.
2. The imaging lens according to claim 1 ,
wherein the fifth lens has a biconcave shape near the optical axis.
3. The imaging lens according to claim 1 ,
wherein the fifth lens has a meniscus shape having a convex surface on the object side near the optical axis.
4. The imaging lens according to claim 1 ,
wherein a conditional expression (5) below is satisfied:
0.7< ih/f< 1.0 (5)
where
ih: maximum image height
f: focal length of the overall optical system of the imaging lens.
5. The imaging lens according to claim 1 ,
wherein conditional expressions (6) and (7) below are satisfied:
0.9< TLA/f< 1.45 (6)
0.24< bf/f< 0.41 (7)
where
TLA: distance on the optical axis from the object-side surface of an optical element nearest to the object to the image plane in which filters are removed
bf: distance on the optical axis from the image-side surface of the fifth lens to the image plane in which filters are removed
f: focal length of the overall optical system of the imaging lens.
6. The imaging lens according to claim 1 ,
wherein a conditional expression (8) below is satisfied:
f 4< f 1 (8)
where
f1: focal length of the first lens
f4: focal length of the fourth lens.
7. The imaging lens according to claim 1 ,
wherein a conditional expression (9) below is satisfied:
0.50< r 4/ f< 1.0 (9)
where
r4: curvature radius of the image-side surface of the second lens
f: focal length of the overall optical system of the imaging lens.