Imaging lens
An imaging lens comprising, in order from the object side: an aperture stop; a positive first lens having convex object-side and image-side surfaces; a double-sided aspheric negative second lens having a concave object-side surface; a meniscus double-sided aspheric positive third lens having a convex image-side surface; and a meniscus double-sided aspheric negative fourth lens having a concave image-side surface. All of the lenses are made of a plastic material.
1. A fixed-focus imaging lens which forms an image of an object on a solid-state image sensor, in which elements are arranged in order from an object side to an image side, comprising:
an aperture stop;
a first lens with positive refractive power having convex surfaces on the object side and the image side;
a second lens as a double-sided aspheric lens with negative refractive power having a concave surface on the object side near an optical axis;
a third lens as a meniscus double-sided aspheric lens with positive refractive power having a convex surface on the image side near the optical axis; and
a fourth lens as a meniscus double-sided aspheric lens with negative refractive power having a concave surface on the image side near the optical axis,
wherein all the lenses are made of plastic material; and
wherein conditional expressions (1), (2), (3), and (4) below are satisfied;
0.56 <r 1 /f< 1.10 (1)
0.86 <f 1 /f 3<1.41 (2)
−5.0 <r 3 /r 4<0.1 (3)
2.0 <r 7 /r 8<4.8 (4)
where
f: focal length of the overall optical system of the imaging lens
f1: focal length of the first lens
f3: focal length of the third lens
r1: curvature radius of the object-side surface of the first lens
r3: curvature radius of the object-side surface of the second lens
r4: curvature radius of the image-side surface of the second lens
r7: curvature radius of the object-side surface of the fourth lens
r8: curvature radius of the image-side surface of the fourth lens.
2. The imaging lens according to claim 1 , wherein a conditional expression (5) below is satisfied:
−1.5 <r 1 /r 2<−0.4 (5)
where
r1: curvature radius of the object-side surface of the first lens
r2: curvature radius of the image-side surface of the first lens.
3. The imaging lens according to claim 1 , wherein a conditional expression (6) below is satisfied:
1.66 <r 5 /r 6<3.20 (6)
where
r5: curvature radius of the object-side surface of the third lens
r6: curvature radius of the image-side surface of the third lens.
4. The imaging lens according to claim 1 , wherein a conditional expression (13) below is satisfied:
0.36 <f 12 /f 34<2.47 (13)
where
f12: composite focal length of the first and second lenses
f34: composite focal length of the third and fourth lenses.
5. The imaging lens according to claim 1 , wherein a conditional expression (14) below is satisfied:
1.80 <f /EPD<2.60 (14)
where
EPD: exit pupil diameter.
6. The imaging lens according to claim 1 , wherein conditional expressions (7), (8), (9), and (10) below are satisfied:
1.50 <Nd 1<1.59 (7)
55.0 νd 1<57.0 (8)
1.60 <Nd 2<1.67 (9)
23.0 <νd 2<26.0 (10)
where
Nd1: refractive index of the first lens at d-ray
νd1: Abbe number of the first lens at d-dray
Nd2: refractive index of the second lens at d-ray
νd2: Abbe number of the second lens at d-dray.
7. The imaging lens according to claim 6 , wherein regarding the refractive indices and Abbe numbers of the first lens and the second lens, conditional expressions (11) and (12) below are satisfied:
1.00 <Nd 2 /Nd 1<1.10 (11)
2.1 <νd 1 /νd 2<2.5 (12).