Imaging lens, imaging apparatus and portable terminal device
View Patent ↗An imaging lens is provided and includes: in order from the object side, a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a concave surface on the image side near the optical axis and having a positive refractive power; a fourth lens having a positive refractive power near the optical axis; and a fifth lens having a negative refractive power near the optical axis. An image side surface of the fifth lens is concave near the optical axis and has a region where a negative power of the region decreases toward a periphery of the fifth lens as compared with a negative power near the optical axis.
1. An imaging lens comprising: in order from an object side,
a first lens having a positive refractive power;
a second lens having a negative refractive power;
a third lens having a concave surface on an image side near an optical axis thereof and having a positive refractive power;
a fourth lens having a positive refractive power near the optical axis thereof; and
a fifth lens having a negative refractive power near the optical axis thereof, wherein an image side surface of the fifth lens is concave near the optical axis and has a region where a negative power of the region decreases toward a periphery of the fifth lens as compared with a negative power near the optical axis, wherein
the following conditional expression is satisfied:
0.8 <f/f 1<1.5,
wherein f1 is a focal length of the first lens, and f is a focal length of the imaging system.
2. The imaging lens according to claim 1 , wherein an object side surface of the first lens is convex toward the object side near the optical axis, and an image side surface of the fourth lens is convex toward an image side near the optical axis.
3. The imaging lens according to claim 1 , wherein the fifth lens is biconcave near the optical axis.
4. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
D7>D6,
wherein D6 is a thickness of the third lens on the optical axis, and D7 is an air space between the third lens and the fourth lens on the optical axis.
5. The imaging lens according to claim 1 , wherein the following conditional expression is further satisfied:
f 1<| f 2|< f 3,
wherein f1 is a focal length of the first lens, f2 is a focal length of the second lens, and f3 is a focal length of the third lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression is further satisfied:
vd2<35,
wherein vd2 is an Abbe number of the second lens at the d-line.
7. The imaging lens according to claim 1 , wherein the following conditional expressions are satisfied:
f4<f1,
f 4<| f 2|, and
f4<f3,
wherein f1 is a focal length of the first lens, f2 is a focal length of the second lens, f3 is a focal length of the third lens, and f4 is a focal length of the fourth lens.
8. The imaging lens according to claim 1 , wherein both surfaces in each of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are aspheric.
9. The imaging lens according to claim 1 , wherein an object side surface of the fifth lens is aspheric and has an inflection point in an effective diameter thereof.
10. The imaging lens according to claim 1 , wherein the image side surface of the fifth lens has an aspheric shape having an inflection point in the effective diameter thereof.
11. The imaging lens according to claim 1 , wherein the image side surface of the fifth lens is aspheric and has a local maximum or minimum point at a position other than the optical axis in the effective diameter thereof.
12. An imaging apparatus comprising:
an imaging lens according to claim 1 ; and
an imaging device for outputting an imaging signal based on an optical image formed by the imaging lens.
13. The imaging apparatus according to claim 12 , wherein the imaging device has a pixel number of 2 mega or more and has a pixel pitch of 3 μm or less.
14. A portable terminal device comprising:
an imaging apparatus according to claim 12 ; and
a display unit that displays an image taken by the imaging apparatus.
15. An imaging lens comprising: in order from an object side,
a first lens having a positive refractive power;
a second lens having a negative refractive power;
a third lens having a concave surface on an image side near an optical axis thereof and having a positive refractive power;
a fourth lens having a positive refractive power near the optical axis thereof; and
a fifth lens having a negative refractive power near the optical axis thereof, wherein an image side surface of the fifth lens is concave near the optical axis and has a region where a negative power of the region decreases toward a periphery of the fifth lens as compared with a negative power near the optical axis, wherein
the following conditional expression is satisfied:
f 1<| f 2|< f 3,
wherein f1 is a focal length of the first lens, f2 is a focal length of the second lens, and f3 is a focal length of the third lens.
16. The imaging lens according to claim 15 , wherein an object side surface of the first lens is convex toward the object side near the optical axis, and an image side surface of the fourth lens is convex toward an image side near the optical axis.
17. The imaging lens according to claim 15 , wherein the fifth lens is biconcave near the optical axis.
18. The imaging lens according to claim 15 , wherein the following conditional expression is satisfied:
D7>D6,
wherein D6 is a thickness of the third lens on the optical axis, and D7 is an air space between the third lens and the fourth lens on the optical axis.
19. The imaging lens according to claim 15 , wherein the following conditional expression is further satisfied:
0.8 <f/f 1<1.5,
wherein f1 is a focal length of the first lens, and f is a focal length of the imaging system.
20. The imaging lens according to claim 15 , wherein the following conditional expression is further satisfied:
vd2<35,
wherein vd2 is an Abbe number of the second lens at the d-line.
21. The imaging lens according to claim 15 , wherein the following conditional expressions are satisfied:
f4<f1,
f 4<| f 2|, and
f4<f3,
wherein f1 is a focal length of the first lens, f2 is a focal length of the second lens, f3 is a focal length of the third lens, and f4 is a focal length of the fourth lens.
22. The imaging lens according to claim 15 , wherein both surfaces in each of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are aspheric.
23. The imaging lens according to claim 15 , wherein an object side surface of the fifth lens is aspheric and has an inflection point in an effective diameter thereof.
24. The imaging lens according to claim 15 , wherein the image side surface of the fifth lens has an aspheric shape having an inflection point in the effective diameter thereof.
25. The imaging lens according to claim 15 , wherein the image side surface of the fifth lens is aspheric and has a local maximum or minimum point at a position other than the optical axis in the effective diameter thereof.
26. An imaging apparatus comprising:
an imaging lens according to claim 15 ; and
an imaging device for outputting an imaging signal based on an optical image formed by the imaging lens.
27. The imaging apparatus according to claim 26 , wherein the imaging device has a pixel number of 2 mega or more and has a pixel pitch of 3 μm or less.
28. A portable terminal device comprising:
an imaging apparatus according to claim 26 ; and
a display unit that displays an image taken by the imaging apparatus.