Small imaging lens and imaging apparatus
An imaging lens includes sequentially, from an object side, a first lens group, a second lens group, a third lens group, and a fourth lens group. The first lens group includes only a first lens having a meniscus shape with a concave surface facing the object side. The second lens group has positive refracting power as a whole and includes sequentially, from the object side, a second-first lens having positive refracting power and a second-second lens cemented to or separated from the second-first lens and having negative refracting power. The third lens group includes only a third lens having a meniscus shape with a concave surface facing the object side. The fourth lens group includes only a fourth lens.
1. An imaging lens system comprising:
a first lens group consisting of a first-first lens, in which the first-first lens has a concave surface facing an object side;
a second lens group having positive refracting power as a whole, said second lens group consisting of a second-first lens having positive refracting power and a second-second lens having negative refracting power, the second-first lens and the second-second lens are sequentially arranged from the object side, and the second-second lens is cemented to or separated from the second-first lens;
a third lens group consisting of a third-first lens, in which the third-first lens has a meniscus shape with a concave surface facing the object side; and
a fourth lens group consisting of a fourth-first lens,
wherein the above lens groups are sequentially arranged from the object side and said imaging lens system has a single fixed focal length.
2. The system of claim 1 , wherein an aperture stop is placed on the object side of said first lens group.
3. The system of claim 1 , wherein an aperture stop is placed between said first lens group and said second lens group.
4. The system of claim 1 , wherein the second-first lens has a biconvex shape, the second-second lens has a biconcave shape, and each of said third-first lens and said fourth-first lens has at least one aspherical surface.
5. The system of claim 1 , wherein the following inequality is satisfied:
0.5< f 12/ f <2.0 (1)
where f 12 is a composite focal length of said first lens group and said second lens group, and f is the focal length of the whole imaging lens system.
6. The system of claim 1 , wherein the following inequality is satisfied:
0.5< f 2/ f <4.0 (2)
where f 2 is a focal length of said second lens group, and f is the focal length of the whole imaging lens system.
7. The system of claim 1 , wherein the following inequalities are satisfied:
0.5< f 2/ f <3.0 (3)
1.0< TL/f <2.5 (4)
where f 2 is a focal length of said second lens group, f is the focal length of the whole imaging lens system, and TL is a total length of said imaging lens, the total length comprising an on-axis distance from a lens surface located nearest to the object side to an image-side focal point of the whole image lens system or in an imaging lens having an aperture stop placed nearest to the object side, an on-axis distance from a surface of the aperture stop which is located nearest to the object side to an image-side focal point of the whole imaging lens system.
8. The system of claim 1 , wherein the following inequalities are satisfied:
40<ν21<85 (5)
20<ν22<35 (6)
where ν21 is an Abbe number of the 2-1st lens with respect to a d-line, and ν22 is an Abbe number of the 2-2nd lens with respect to a d-line.
9. The system of claim 1 , wherein the following inequality is satisfied:
0.0<2 Y/EP <1.5 (7)
where 2Y is an effective screen diagonal length of a solid-state image sensing device, and EP is an on-axis distance from an exit pupil of the whole imaging lens system to an image-side focal point of the whole imaging lens system.
10. The system of claim 1 , wherein each of lenses forming said first lens group, said third lens group, and said fourth lens group includes at least one aspherical surface.
11. The system of claim 1 , wherein said imaging lens system is a five element/four group imaging lens system.
12. An imaging apparatus comprising an imaging lens system and a solid-state image sensing device, wherein the image lens system comprises:
a first lens group consisting of a first-first lens, in which the first-first lens has a concave surface facing an object side;
a second lens group having positive refracting power as a whole, said second lens group consisting of a second-first lens having positive refracting power and a second-second lens having negative refracting power, the second-first lens and the second-second lens are sequentially arranged from the object side, and the second-second lens is cemented to or separated from the second-first lens;
a third lens group consisting of a third-first lens, in which the third-first lens has a meniscus shape with a concave surface facing the object side; and
a fourth lens group consisting of a fourth-first lens,
wherein the above lens groups are sequentially arranged from the object side and said imaging lens system has a single fixed focal length.
13. The apparatus of claim 12 , wherein an aperture stop is placed on the object side of said first lens group.
14. The apparatus of claim 12 , wherein an aperture stop is placed between said first lens group and said second lens group.
15. The apparatus of claim 12 , wherein the second-first lens has a biconvex shape, the second-second lens has a biconcave shape, and each of said third-first lens and said fourth-first lens has at least one aspherical surface.
16. The apparatus of claim 12 , wherein the following inequality is satisfied:
0.5< f 12/ f 21 2.0 (1)
where f 12 is a composite focal length of said first lens group and said second lens group, and f is the focal length of the whole imaging lens system.
17. The apparatus of claim 12 , wherein the following inequality is satisfied:
0.5< f 2/ f <4.0 (2)
where f 2 is a focal length of said second lens group, and f is the focal length of the whole imaging lens system.
18. The apparatus of claim 12 , wherein the following inequalities are satisfied:
0.5< f 2/ f <3.0 (3)
1.0< TL/f 21 2.5 (4)
where f 2 is a focal length of said second lens group, f is the focal length of the whole imaging lens system, and TL is a total length of said imaging lens, the total length comprising an on-axis distance from a lens surface located nearest to the object side to an 15 image-side focal point of the whole image lens system or in an imaging lens having an aperture stop placed nearest to the object side, an on-axis distance from a surface of the aperture stop which is located nearest to the object side to an image-side focal point of the whole imaging lens system.
19. The apparatus of claim 12 , wherein the following inequalities are satisfied:
40<ν21<85 (5)
20<ν22<35 (6)
where ν21 is an Abbe number of the 2-1st lens with respect to a d-line, and ν22 is an Abbe number of the 2-2nd lens with respect to a d-line.
20. The apparatus of claim 12 , wherein the following inequality is satisfied:
0.0<2 Y/EP <1.5 (7)
where 2Y is an effective screen diagonal length of the solid-state image sensing device, and EP is an on-axis distance from an exit pupil of the whole imaging lens system to an image-side focal point of the whole imaging lens system.
21. The apparatus of claim 12 , wherein each of lenses forming said first lens group, said third lens group, and said fourth lens group includes at least one aspherical surface.
22. The apparatus of claim 12 , wherein said imaging lens system is a five element/four group imaging lens system.