Imaging lens
There is provided an imaging lens with excellent optical characteristics which satisfies demand of a low profile and a low F-number. An imaging lens comprises in order from an object side to an image side, a first lens with positive refractive power being formed in a meniscus shape having an object-side surface being convex in a paraxial region, a second lens with negative refractive power in a paraxial region, a third lens with positive refractive power having an object-side surface being concave in a paraxial region, and a fourth lens with negative refractive power having an image-side surface being concave 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 being formed in a meniscus shape having an object-side surface being convex in a paraxial region,
a second lens with negative refractive power in a paraxial region,
a third lens with positive refractive power having an object-side surface being concave in a paraxial region, and
a fourth lens with negative refractive power having an image-side surface being concave in a paraxial region,
wherein the following conditional expressions (1), (2), (3), (4) and 18 are satisfied:
9.00< νd 2<29.00 (1)
0.55< r 2/ f< 5.25 (2)
2.15< r 4/ f< 6.00 (3)
35.50< r 7/ T 3<235.00 (4)
5.00<( D 1/ f 1)×100<14.00 (18)
where
νd2: an abbe number at d-ray of the second lens,
r2: a paraxial curvature radius of an image-side surface of the first lens, f: a focal length of an overall optical system of the imaging lens,
r4: a paraxial curvature radius of an image-side surface of the second lens,
r7: a paraxial curvature radius of an object-side surface of the fourth lens,
T3: a distance along the optical axis from an image-side surface of the third lens to an object-side surface of the fourth lens,
D1: a thickness along the optical axis of the first lens, and
f1: a focal length of the first lens.
2. The imaging lens according to claim 1 , wherein an object-side surface of said second lens is concave in the paraxial region.
3. The imaging lens according to claim 1 , wherein the following conditional expression (5) is satisfied:
2.50<( T 2/ f )×100<10.50 (5)
where
T2: a distance along the optical axis from an image-side surface of the second lens to an object-side surface of the third lens, and
f: a focal length of the overall optical system of the imaging lens.
4. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
8.00 <r 7/ T 2<65.00 (6)
where
r7: a paraxial curvature radius of an object-side surface of the fourth lens, and
T2: a distance along the optical axis from an image-side surface of the second lens to an object-side surface of the third lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression (7) is satisfied:
5.00 <r 2/ r 8<18.00 (7)
where
r2: a paraxial curvature radius of an image-side surface of the first lens, and r8: a paraxial curvature radius of an image-side surface of the fourth lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression (8) is satisfied:
5.00 <r 4/ r 8<20.00 (8)
where
r4: a paraxial curvature radius of an image-side surface of the second lens, and r8: a paraxial curvature radius of an image-side surface of the fourth lens.
7. The imaging lens according to claim 1 , wherein the following conditional expression (9) is satisfied:
2.95 <f 2/ f 4<5.70 (9)
where
f2: a focal length of the second lens, and f4: a focal length of the fourth lens.