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, a second lens with positive refractive power, a third lens with positive refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, a sixth lens, and a seventh lens with negative refractive power, wherein said fourth lens has an image-side surface being convex in a paraxial region, said seventh lens has 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 negative refractive power,
a second lens with positive refractive power,
a third lens with positive refractive power,
a fourth lens with negative refractive power,
a fifth lens with positive refractive power,
a sixth lens, and
a seventh lens with negative refractive power,
wherein said fourth lens has an image-side surface being convex in a paraxial region, said seventh lens has an image-side surface being concave in a paraxial region, and the following conditional expressions (1), (2) and (3) are satisfied:
−1.90< f 7/ f<− 0.30 (1)
41.00<| r 2|/ D 1 (2)
1.00< r 11/( T 5+ D 6)<20.00 (3)
where,
f7: a focal length of the seventh lens,
f: a focal length of the overall optical system of the imaging lens,
r2: a paraxial curvature radius of an image-side surface of the first lens,
D1: a thickness along the optical axis of the first lens,
r11: a paraxial curvature radius of an object-side surface of the sixth lens,
T5: a distance along the optical axis from an image-side surface of the fifth lens to an object-side surface of the sixth lens, and
D6: a thickness along the optical axis of the sixth lens.
2. The imaging lens according to claim 1 , wherein an image-side surface of said third lens is convex in a paraxial region.
3. The imaging lens according to claim 1 , wherein the following conditional expression (4) is satisfied:
0.35< f 5/ f< 1.58 (4)
where
f5: a focal length of the fifth lens.
4. The imaging lens according to claim 1 , wherein the following conditional expression (5) is satisfied:
−1.70< r 6/ f<− 0.20 (5)
where
r6: a paraxial curvature radius of an image-side surface of the third lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
1.10<| r 9|/ f< 7.00 (6)
where
r9: a paraxial curvature radius of an object-side surface of the fifth lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression (7) is satisfied:
3.50< r 13/ T 6<12.50 (7)
where
r13: a paraxial curvature radius of an object-side surface of the seventh lens, and
T6: a distance along the optical axis from an image-side surface of the sixth lens to an object-side surface of the seventh lens.
7. The imaging lens according to claim 1 , wherein the following conditional expression (8) is satisfied:
−1.70< r 13/ f 7<−0.45 (8)
where r13: a paraxial curvature radius of an object-side surface of the seventh lens.