Imaging lens
The present invention includes, from an object side to an image-plane side: an aperture stop with a predetermined diameter, a first lens with a positive refractive power having a convex surface on the object side, a second lens with a positive refractive power having a concave surface on the object side, and a third lens with a negative refractive power having a convex surface on the object side. The second and third lenses have aspherical surfaces on their object-side and image-plane-side surfaces. The third lens is formed with an inflection point where the curvature orientation changes within the effective diameter range of the aspherical surface on the image-plane side. An appropriate back focus is maintained while the total length of the lens system is reduced. A compact, thin, high-performance design is achieved, which effectively corrects various aberrations, especially astigmatism and distortion, and is suited for digital cameras using high-density solid-state imaging elements of one million pixels or more.
1. An imaging lens comprising, in sequence from an object side to an image plane side:
an aperture stop with a predetermined diameter;
a first lens with an overall positive refractive power having a convex surface facing toward the object side;
a second lens with an overall positive refractive power having a concave surface facing toward the object side; and
a third lens with an overall negative refractive power having a concave surface facing toward the object side;
wherein the imaging lens includes only three lenses, the first lens, the second lens, and the third lens;
wherein said second lens is formed with aspherical surfaces on said object side surface and an image plane side surface; and
wherein said third lens is formed with aspherical surfaces on said object side surface and an image plane side surface and is formed with an inflection point, where a curvature orientation changes, within an effective diameter range of said aspherical surface on said image plane side surface.
2. An imaging lens comprising, in sequence from an object side to an image plane side:
an aperture stop with a predetermined diameter;
a first lens with an overall positive refractive power having a convex surface facing toward the object side and having a meniscus shape with said convex surface facing toward the object side and a concave surface facing toward the image plane side;
a second lens with an overall positive refractive power having a concave surface facing toward the object side; and
a third lens with an overall negative refractive power having a concave surface facing toward the object side;
wherein said second lens is formed with aspherical surfaces on said object side surface and an image plane side surface; and
wherein said third lens is formed with aspherical surfaces on said object side surface and an image plane side surface and is formed with an inflection point, where a curvature orientation changes, within an effective diameter range of said aspherical surface on said image plane side surface.
3. An imaging lens as described in claim 1 wherein said object-side aspherical surface of said third lens is formed so that a refractive power thereof increases toward a perimeter section thereof.
4. An imaging lens as described in claim 1 wherein said second lens and said third lens are formed from a resin material.
5. An imaging lens as described in claim 1 wherein:
TL/f< 1.4
where f is a focal length of a lens system, and TL is a total length of said lens system from said aperture stop to said image plane.
6. An imaging lens comprising, in sequence from an object side to an image plane side:
an aperture stop with a predetermined diameter;
a first lens with an overall positive refractive power having a convex surface facing toward the object side;
a second lens with an overall positive refractive power having a concave surface facing toward the object side; and
a third lens with an overall negative refractive power having a concave surface facing toward the object side;
wherein said second lens is formed with aspherical surfaces on said object side surface and an image plane side surface;
wherein said third lens is formed with aspherical surfaces on said object side surface and an image plane side surface and is formed with an inflection point, where a curvature orientation changes, within an effective diameter range of said aspherical surface on said image plane side surface; and wherein:
v 1>45, v 2>45, v 3<45
where v1 is the Abbe number of said first lens, v2 is the Abbe number of said second lens, and v3 is the Abbe number of said third lens.
7. An imaging lens comprising, in sequence from an object side to an image plane side:
an aperture stop with a predetermined diameter;
a first lens with an overall positive refractive power having a convex surface facing toward the object side;
a second lens with an overall positive refractive power having a concave surface facing toward the object side; and
a third lens with an overall negative refractive power having a concave surface facing toward the object side;
wherein said second lens is formed with aspherical surfaces on said object side surface and an image plane side surface;
wherein said third lens is formed with aspherical surfaces on said object side surface and an image plane side surface and is formed with an inflection point, where a curvature orientation changes, within an effective diameter range of said aspherical surface on said image plane side surface; and wherein:
1<| R 4|/| R 5|<2
6<| R 6|/| R 7|<10
where R 4 is a curvature radius of said object-side surface of said second lens, R 5 is a curvature radius of said image-plane side surface of said second lens, R 6 is a curvature radius of said object-side surface of said third lens, and R 7 is a curvature radius of said image-plane side surface of said third lens.
8. An imaging lens as described in claim 1 wherein:
D 5/ f< 0.15
where f is a focal length of a lens system, and D 5 is a distance along an optical axis between said second lens and said third lens.
9. An imaging lens comprising, in sequence from an object side to an image plane side:
an aperture stop with a predetermined diameter;
a first lens with an overall positive refractive power having a convex surface facing toward the object side;
a second lens with an overall positive refractive power having a concave surface facing toward the object side; and
a third lens with an overall negative refractive power having a concave surface facing toward the object side;
wherein said second lens is formed with aspherical surfaces on said object side surface and an image plane side surface;
wherein said third lens is formed with aspherical surfaces on said object side surface and an image plane side surface and is formed with an inflection point, where a curvature orientation changes, within an effective diameter range of said aspherical surface on said image plane side surface; and wherein:
0.45< D 4/ D 6<1.0
where D 4 is a thickness along an optical axis of said second lens and D 6 is a thickness along said optical axis of said third lens.
10. An imaging lens as described in claim 2 wherein said object-side aspherical surface of said third lens is formed so that a refractive power thereof increases toward a perimeter section thereof.
11. An imaging lens as described in claim 2 wherein said second lens and said third lens are formed from a resin material.
12. An imaging lens as described in claim 3 wherein said second lens and said third lens are formed from a resin material.
13. An imaging lens as described in claim 2 wherein:
TL/f< 1.4
where f is a focal length of a lens system, and TL is a total length of said lens system from said aperture stop to said image plane.
14. An imaging lens as described in claim 3 wherein:
TL/f< 1.4
where f is a focal length of a lens system, and TL is a total length of said lens system from said aperture stop to said image plane.
15. An imaging lens as described in claim 4 wherein:
TL/f< 1.4
where f is a focal length of a lens system, and TL is a total length of said lens system from said aperture stop to said image plane.
16. An imaging lens as described in claim 2 wherein:
v 1>45, v 2>45, v 3<45
where v1 is the Abbe number of said first lens, v2 is the Abbe number of said second lens, and v3 is the Abbe number of said third lens.
17. An imaging lens as described in claim 3 wherein:
v 1>45, v 2>45, v 3<45
where v1 is the Abbe number of said first lens, v2 is the Abbe number of said second lens, and v3 is the Abbe number of said third lens.
18. An imaging lens as described in claim 4 wherein:
v 1>45, v 2>45, v 3<45
where v1 is the Abbe number of said first lens, v2 is the Abbe number of said second lens, and v3 is the Abbe number of said third lens.
19. An imaging lens as described in claim 5 wherein:
v 1>45, v 2>45, v 3<45
where v1 is the Abbe number of said first lens, v2 is the Abbe number of said second lens, and v3 is the Abbe number of said third lens.