Photographic lens
View Patent ↗A small size photographic lens for the photographic unit of a device such as a camera or a camera phone. The photographic lens includes: a first lens having positive refractive power; a second lens having negative refractive power and a convex surface facing the object side; a third lens having positive refractive power; and a fourth lens having negative refractive power at the center portion, in which the negative refractive power becomes weaker from the center portion toward the peripheral portion of the fourth lens, and having a positive refractive power at the peripheral portion thereof, the lenses being numbered in order of location from the object.
1. A photographic lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power and a convex surface facing the object side;
a third lens having positive refractive power; and
a fourth lens having negative refractive power at a center portion, in which the negative refractive power becomes weaker from the center portion toward the peripheral portion of the fourth lens, and having a positive refractive power at the peripheral portion thereof,
wherein the lenses are numbered in order of location from the object side, and,
wherein the condition 0.9≦(r 4 +r 5 )/(r 4 −r 5 )≦1.8 is satisfied,
where r 4 denotes the radius of curvature of the surface of the second lens facing the object side, and r 5 denotes the radius of curvature of the surface of the second lens facing the image side.
2. The photographic lens of claim 1 , wherein the condition 1.4≦f/f 1 ≦1.9 is satisfied,
where f denotes the focal length of the entire photographic lens, and f 1 denotes the focal length of the first lens.
3. The photographic lens of claim 1 , wherein the condition 0.6≦f/|f 2 |≦1.5 is satisfied,
where f denotes the focal length of the entire photographic lens, and f 2 denotes the focal length of the second lens.
4. The photographic lens of claim 1 , further comprising:
an aperture stop disposed between the first lens and the object.
5. The photographic lens of claim 4 , further comprising:
an aperture stop disposed between the first lens and the object.
6. The photographic lens of claim 1 , wherein the condition 20<V 1 −V 2 <50 is satisfied,
where V 1 denotes an Abbe constant of the first lens, and V 2 denotes an Abbe constant of the second lens.
7. The photographic lens of claim 1 , wherein the condition 0.2≦|r 7 |/f≦0.4 is satisfied,
where f denotes the focal length of the entire photographic lens, and r 7 denotes the radius of curvature of the surface of the third lens facing the image side.
8. The photographic lens of claim 1 , wherein the condition 0.5≦r 8 /f≦1.0 is satisfied,
where f denotes the focal length of the entire photographic lens, and r 8 denotes the radius of curvature of the surface of the fourth lens facing the object side.
9. The photographic lens of claim 1 , wherein the fourth lens has at least one aspheric surface.
10. The photographic lens of claim 1 , wherein each of the first through fourth lenses has at least one aspheric surface.
11. The photographic lens of claim 1 , wherein the third lens is a meniscus lens having a convex surface facing the image side.
12. A photographic lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power at a center portion, in which the negative refractive power becomes weaker from the center portion toward the peripheral portion of the second lens, and having a positive refractive power at the peripheral portion thereof;
a third lens having positive refractive power; and
a fourth lens having negative refractive power,
wherein the lenses are numbered in order of location from the object.
13. The photographic lens of claim 12 , wherein the fourth lens has negative refractive power at a center portion, which becomes weaker from the center portion toward the peripheral portion of the fourth lens, and has a positive refractive power at the peripheral portion thereof.
14. The photographic lens of claim 12 , wherein the condition 1.4≦f/f 1 1≦1.9 is satisfied,
where f denotes the focal length of the entire photographic lens, and f 1 denotes the focal length of the first lens.
15. The photographic lens of claim 12 , wherein the condition 0.6≦f/|f 2 |≦1.5 is satisfied,
where f denotes the focal length of the entire photographic lens, and f 2 denotes the focal length of the second lens.
16. The photographic lens of claim 12 , wherein the condition 20<V 1 −V 2 <50 is satisfied,
where V 1 denotes an Abbe constant of the first lens, and V 2 denotes an Abbe constant of the second lens.
17. The photographic lens of claim 12 , wherein the condition 0.2≦|r 7 |/f≦0.4 is satisfied,
where f denotes the focal length of the entire photographic lens, and r 7 denotes the radius of curvature of the surface of the third lens facing the image side.
18. The photographic lens of claim 12 , wherein the condition 0.5≦r 8 /f≦1.0 is satisfied,
where f denotes the focal length of the entire photographic lens, and r 8 denotes the radius of curvature of the surface of the fourth lens facing the object side.
19. The photographic lens of claim 12 , wherein the fourth lens has at least one aspheric surface.
20. The photographic lens of claim 12 , wherein each of the first through fourth lenses has at least one aspheric surface.
21. The photographic lens of claim 12 , wherein the third lens is a meniscus lens having a convex surface facing the image side.
22. The photographic lens of claim 12 , wherein the condition 0.5<(r 4 +r 5 )/(r 4 −r 5 )<1.8 is satisfied,
where r 4 denotes the radius of curvature of the surface of the second lens facing the object, and r 5 denotes the radius of curvature of the surface of the second lens facing the image side.
23. A photographic lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power and a convex surface facing the object side;
a third lens having positive refractive power; and
a fourth lens having negative refractive power at a center portion, in which the negative refractive power becomes weaker from the center portion toward the peripheral portion of the fourth lens, and having a positive refractive power at the peripheral portion thereof,
wherein the lenses are numbered in order of location from the object side.
24. The photographic lens of claim 23 , wherein each of the first through fourth lenses has at least one aspheric surface.