Imaging lens
There is provided an imaging lens with excellent optical characteristics while satisfying demand of low-profileness and low F-number. An imaging lens comprises, in order from an object side to an image side, a first lens with positive refractive power formed in a biconvex shape having an object-side surface and an image-side surface being convex in a paraxial region, a second lens with negative refractive power in a paraxial region, a third lens with the negative refractive power in a paraxial region, a fourth lens with the negative refractive power in a paraxial region, and a fifth lens with the positive refractive power having an image-side surface being convex in a paraxial region, and predetermined conditional expressions are satisfied.
1. An imaging lens comprising in order from an object side to an image side,
a first lens with positive refractive power formed in a biconvex shape having an object-side surface and an image-side surface being convex in a paraxial region,
a second lens with negative refractive power in a paraxial region,
a third lens with the negative refractive power in a paraxial region,
a fourth lens with the negative refractive power in a paraxial region, and
a fifth lens with the positive refractive power having an image-side surface being convex in a paraxial region,
wherein an image-side surface of said third lens is concave in the paraxial region, and the following conditional expressions (1), (2) and (4) are satisfied:
10.00< νd 2<30.00 (1)
0.10<| r 5|/ f< 0.90 (2)
2.00< r 8/ f< 35.00 (4)
where
νd2: an abbe number at d-ray of the second lens,
r5: a paraxial curvature radius of an object-side surface of the third lens,
r8: a paraxial curvature radius of an image-side surface of the fourth lens, and
f: a focal length of the overall optical system of the imaging lens.
2. The imaging lens according to claim 1 , wherein an object-side surface of said second lens is convex in the paraxial region.
3. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
20.50< T 3/ T 4<49.00 (3)
where
T3: a distance along an optical axis from an image-side surface of the third lens to an object-side surface of the fourth lens, and
T4: a distance along an optical axis from an image-side surface of the fourth lens to an object-side surface of the fifth lens.
4. The imaging lens according to claim 1 , wherein the following conditional expression (5) is satisfied:
−1.40< r 10/ f 5<−0.40 (5)
where
r10: a paraxial curvature radius of an image-side surface of the fifth lens, and
f5: a focal length of the fifth lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
−20.00< f 2/ T 2<−5.50 (6)
where
f2: a focal length of the second lens, and
T2: a distance along an optical axis from an image-side surface of the second lens to an object-side surface of the third lens.