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 an object-side surface being convex in a paraxial region; a second lens with negative refractive power having an object-side surface being convex in a paraxial region; a third lens with negative refractive power having an object-side surface being concave in a paraxial region; a fourth lens with negative refractive power in a paraxial region; and a fifth lens with 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 having an object-side surface being convex in a paraxial region;
a second lens with negative refractive power having an object-side surface being convex in a paraxial region;
a third lens with negative refractive power having an object-side surface being concave in a paraxial region;
a fourth lens with negative refractive power in a paraxial region; and
a fifth lens with positive refractive power having an image-side surface being convex in a paraxial region,
wherein the imaging lens has a total of five single lenses, and
the following conditional expressions (1) and (2) are satisfied:
0.90 <|r 7| /f <4.00 (1)
0.15 <r 3 /f< 0.75 (2)
where
r7: a paraxial curvature radius of an object-side surface of the fourth lens,
r3: a paraxial curvature radius of an object-side surface of the second 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 image-side surface of said second lens is concave in the paraxial region.
3. The imaging lens according to claim 1 , wherein an image-side surface of said third lens is convex in the paraxial region.
4. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
1.00 <r 4 /T 2<5.25 (3)
where
r4: a paraxial curvature radius of an image-side surface of the second 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 (4) is satisfied:
−12.00 <r 5 /D 3<−3.00 (4)
where
r5: a paraxial curvature radius of an object-side surface of the third lens, and
D3: a thickness along the optical axis of the third lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression (5) is satisfied:
0.40 <r 3 /r 4<1.80 (5)
where
r3: a paraxial curvature radius of an object-side surface of the second lens, and
r4: a paraxial curvature radius of an image-side surface of the second lens.