Imaging lens
A compact, wide view-field imaging lens with a small F-value which corrects aberrations properly. Its elements are arranged in order from an object side to an image side: an aperture stop, positive first lens having convex surfaces on the object and image sides, negative second lens having a concave object-side surface near an optical axis, positive meniscus third lens having a convex image-side surface, and negative meniscus double-sided aspheric fourth lens having a concave image-side surface near the optical axis. Its F-value is smaller than 2.4 and it satisfies conditional expressions (1) to (3) below: 0.15< f 12/ f 34<0.5 (1) 0.1<| r 1/ r 2|<0.5 (2) 1.0< f 1/ f 3<1.6 (3) where f1: first lens focal length f3: third lens focal length f12: composite focal length of the first and second lenses f34: composite focal length of the third and fourth lenses r1: curvature radius of the first lens object-side surface r2: curvature radius of the first lens image-side surface.
1. An imaging lens for 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 a convex surface on each of the object side and the image side;
a second lens with negative refractive power having a concave surface on the object side near an optical axis;
a third lens with positive refractive power as a meniscus lens having a convex surface on the image side; and
a fourth lens with negative refractive power as a meniscus double-sided aspheric lens having a concave surface on the image side near the optical axis, wherein
an F-value is smaller than 2.4; and
conditional expressions (1) to (3) below are satisfied:
0.15< f 12/ f 34<0.5 (1)
0.1<| r 1/ r 2|<0.5 (2)
1.0< f 1/ f 3<1.6 (3)
where
f1: focal length of the first lens
f3: focal length of the third lens
f12: composite focal length of the first lens and the second lens
f34: composite focal length of the third lens and the fourth lens
r1: curvature radius of the object-side surface of the first lens
r2: curvature radius of the image-side surface of the first lens.
2. The imaging lens according to claim 1 ,
wherein a conditional expression (4) below is satisfied:
−6.5< r 3/ f<− 0.7 (4)
where
f: focal length of an overall optical system of the imaging lens
r3: curvature radius of the object-side surface of the second lens.
3. The imaging lens according to claim 1 ,
wherein a conditional expression (5) below is satisfied:
3.3< r 7/ r 8<7.5 (5)
where
r7: curvature radius of the object-side surface of the fourth lens
r8: curvature radius of the image-side surface of the fourth lens.
4. The imaging lens according to claim 1 ,
wherein a conditional expression (6) below is satisfied:
TLA/ 2 ih< 0.9 (6)
where
TLA: distance on the optical axis from the object-side surface of an optical element located nearest to the object to an image plane with a filter or the like removed
ih: maximum image height.
5. The imaging lens according to claim 1 ,
wherein a conditional expression (7) below is satisfied:
ih/f> 0.7 (7)
where
f: focal length of an overall optical system of the imaging lens
ih: maximum image height.