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 negative refractive power having an object-side surface being convex in a paraxial region, a second lens with positive refractive power in a paraxial region, a third lens with the negative refractive power in a paraxial region, a fourth lens with the positive refractive power in a paraxial region, a fifth lens having a flat object-side surface and a flat image-side surface that are aspheric, and a sixth lens with the negative refractive power having an image-side surface being concave in a paraxial region.
1. An imaging lens comprising, in order from an object side to an image side,
a first lens with negative refractive power having an object-side surface being convex in a paraxial region,
a second lens with positive refractive power in a paraxial region,
a third lens with negative refractive power in a paraxial region,
a fourth lens with positive refractive power in a paraxial region,
a fifth lens having a flat object-side surface and a flat image-side surface that are aspheric, and a sixth lens with negative refractive power having an image-side surface being concave in a paraxial region,
wherein the following conditional expressions (4), (5), (13), (15), and (18′) are satisfied:
−2.45< r 2/ r 4<−0.45 (4)
0.65< r 1/ f< 4.00 (5)
| r 3|/ r 4≤−2.51 (13)
30.00< r 2/ T 2 (15)
−0.58<= r 8/ f<− 0.15 (18′)
where
r1: a paraxial curvature radius of an object-side surface of the first lens,
r2: a paraxial curvature radius of an image-side surface of the first lens,
r3: a paraxial curvature radius of an object-side surface of the second lens,
r4: a paraxial curvature radius of an image-side surface of the second lens,
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,
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 the following conditional expression (1) is satisfied:
−9.55<( T 1/ f 1)×100<−1.00 (1)
where
T1: a distance along the optical axis from an image-side surface of the first lens to an object-side surface of the second lens, and
f1: a focal length of the first lens.
3. The imaging lens according to claim 1 , wherein the following conditional expression (2) is satisfied:
0.02< T 2/ T 3<0.60 (2)
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
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.
4. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
−15.50< f 6/ D 6<−1.50 (3)
where
f6: a focal length of the sixth lens, and
D6: a thickness along the optical axis of the sixth lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
0.80< r 12/ D 6<3.00 (6)
where
r12: a paraxial curvature radius of an image-side surface of the sixth lens, and
D6: a thickness along the optical axis of the sixth lens.