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 having a convex object-side surface in a paraxial region, a second lens with negative refractive power having a concave image-side surface in a paraxial region, a third lens having a convex object-side surface in a paraxial region, a fourth lens having a convex image-side surface in a paraxial region, a fifth lens having a convex object-side surface in a paraxial region, and a sixth lens having a concave image-side surface in a paraxial region, wherein three out of four lenses from the third lens to the sixth lens have positive refractive power or negative refractive power in the paraxial region, and one out of four lenses is formed in a meniscus shape, substantially has no refractive power in the paraxial region, and has aspheric surfaces on both sides, and a predetermined conditional expression is satisfied.
1. An imaging lens comprising, in order from an object side to an image side, a first lens with positive refractive power having a convex object-side surface in a paraxial region, a second lens with negative refractive power having a concave image-side surface in a paraxial region,
a third lens having a convex object-side surface in a paraxial region,
a fourth lens having a convex image-side surface in a paraxial region,
a fifth lens with positive refractive power having a convex object-side surface in a paraxial region, and
a sixth lens having a concave image-side surface in a paraxial region,
wherein three out of four lenses from the third lens to the sixth lens have positive refractive power or negative refractive power in the paraxial region, and
one out of the four lenses is formed in a meniscus shape in the paraxial region, substantially has no refractive power in the paraxial region, and has aspheric surfaces on both sides, and the following conditional expressions (1) and (5) are satisfied:
1 E 6 mm<| fCNE |mm (1)
8.30<( D 1/ f 1)×100<13.00 (5)
where
fCNE: a focal length of a lens substantially having no refractive power,
D1: a thickness of the first lens along the optical axis, and
F1: a focal length of the first lens.
2. The imaging lens according to claim 1 , wherein an image-side surface of said first lens is concave in a paraxial region.
3. The imaging lens according to claim 1 , wherein an object-side surface of said sixth lens is convex in a paraxial region.
4. The imaging lens according to claim 1 , wherein the following conditional expression (2) is satisfied:
|( nCNE −1)×(1 /CNEr 1−1 /CNEr 2)+( nCNE −1) 2 ×dCNE/nCNE/CNEr 1 /CNEr 2|<1 E −6 (2)
where
|nCNE: a refractive index at d-ray of a lens substantially having no refractive power,
CNEr1: a paraxial curvature radius of an object-side surface of a lens substantially having no refractive power,
CNEr2: a paraxial curvature radius of an image-side surface of a lens substantially having no refractive power, and
dCNE: a thickness along the optical axis of a lens substantially having no refractive power.
5. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
1 E 6 <|fCNE +(− CNEr 1 ×dCNE /( CNEr 2 −CNEr 1 +dCNE ))| (3)
where
fCNE: a focal length of a lens substantially having no refractive power,
CNEr1: a paraxial curvature radius of an object-side surface of a lens substantially having no refractive power,
CNEr2: a paraxial curvature radius of an image-side surface of a lens substantially having no refractive power, and
dCNE: a thickness along the optical axis of a lens substantially having no refractive power.
6. The imaging lens according to claim 1 , wherein the following conditional expression (4) is satisfied:
39 <vd 5<73 (4)
where
vd5: an abbe number at d-ray of the fifth lens.
7. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
−4.35<( T 1/ f 2)×100<−2.00 (6)
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
f2: a focal length of the second lens.
8. The imaging lens according to claim 1 , wherein the following conditional expression (7) is satisfied:
0.20<| r 6|/ f< 1.55 (7)
where
r6: a paraxial curvature radius of an image-side surface of the third lens, and f: a focal length of the overall optical system of the imaging lens.