Imaging lens composed of six optical elements
A compact, low-profile, low-cost imaging lens with an F-value of 2.5 or less and a wide field of view which corrects aberrations properly. Its elements are arranged from an object side to an image side: a first positive optical element group including a first positive lens having a convex object-side surface, a second negative lens having a concave image-side surface, and a third positive lens having a convex object-side surface; a second positive optical element group including a fourth positive lens having a convex image-side surface; and a third negative optical element group including a fifth negative double-sided aspheric lens having a concave image-side surface. The fifth lens image-side surface has at least one pole-change point off an optical axis. A double-sided aspheric aberration correction optical element with virtually no refractive power is located in an air gap nearer to the image plane than the first optical element group.
1. An imaging lens composed of six optical elements which forms an image of an object on a solid-state image sensor, in which the elements are arranged in order from an object side to an image side, the imaging lens comprising:
a first optical element group with positive refractive power including:
a first lens with positive refractive power having a convex surface on the object side as a first optical element;
a second lens with negative refractive power having a concave surface on the image side as a second optical element; and
a third lens with positive refractive power having a convex surface on the object side as a third optical element;
a second optical element group with positive refractive power including a fourth lens with positive refractive power having a convex surface on the image side as a fourth optical element; and
a third optical element group with negative refractive power including a double-sided aspheric fifth lens with negative refractive power having a concave surface on the image side as a fifth optical element, wherein
at least one pole-change point is formed off an optical axis on the image-side surface of the fifth lens; and
a double-sided aspheric aberration correction optical element which has a flat surface near the optical axis with virtually no refractive power as a sixth optical element is located in an air gap nearer to an image plane than the first optical element group.
2. An imaging lens composed of six optical elements which forms an image of an object on a solid-state image sensor, in which the elements are arranged in order from an object side to an image side, the imaging lens comprising:
a first optical element group with positive refractive power including:
a first lens with positive refractive power having a convex surface on the object side as a first optical element;
a second lens with positive refractive power having a convex surface on the object side as a second optical element; and
a third lens with negative refractive power having a concave surface on the image side as a third optical element;
a second optical element group with positive refractive power including a fourth lens with positive refractive power having a convex surface on the image side as a fourth optical element; and
a third optical element group with negative refractive power including a double-sided aspheric fifth lens with negative refractive power having a concave surface on the image side as a fifth optical element, wherein
at least one pole-change point is formed off an optical axis on the image-side surface of the fifth lens; and
a double-sided aspheric aberration correction optical element which has a flat surface near the optical axis with virtually no refractive power as a sixth optical element is located in an air gap nearer to an image plane than the first optical element group.
3. The imaging lens composed of six optical elements according to claim 1 , wherein the aberration correction optical element is located between the first optical element group and the second optical element group.
4. The imaging lens composed of six optical elements according to claim 1 , wherein the aberration correction optical element is located between the second optical element group and the third optical element group.
5. The imaging lens composed of six optical elements according to claim 1 , wherein the aberration correction optical element is located on the image side of the third optical element group.
6. The imaging lens composed of six optical elements according to claim 1 , wherein conditional expressions (1) and (2) below are satisfied:
0.1< TN/f< 0.5 (1)
40<ν dN< 60 (2)
where
TN: distance on the optical axis of an air gap where the aberration correction optical element is located
f: focal length of an overall optical system of the imaging lens
νdN: Abbe number of the aberration correction optical element at d-ray.
7. The imaging lens composed of six optical elements according to claim 1 , wherein aspheric surfaces on both sides of the aberration correction optical element are shaped so as to curve toward the object side with increasing distance from the optical axis.
8. The imaging lens composed of six optical elements according to claim 1 , wherein a conditional expression (3) below is satisfied:
1.0< fLG 1/ f< 2.0 (3)
where
fLG 1 : focal length of the first optical element group
f: focal length of an overall optical system of the imaging lens.
9. The imaging lens composed of six optical elements according to claim 1 , wherein a conditional expression (4) below is satisfied:
0.3< fLG 2/ f< 1.0 (4)
where
fLG 2 : focal length of the second optical element group
f: focal length of an overall optical system of the imaging lens.
10. The imaging lens composed of six optical elements according to claim 1 , wherein a conditional expression (5) below is satisfied:
−0.8< fLG 3/ f<− 0.2 (5)
where
fLG 3 : focal length of the third optical element group
f: focal length of an overall optical system of the imaging lens.
11. The imaging lens composed of six optical elements according to claim 1 , wherein a conditional expression (6) below is satisfied:
0.8<( r 7+ r 8)/( r 7− r 8)<4.5 (6)
where
r 7 : curvature radius of the object-side surface of the fourth lens constituting the second optical element group
r 8 : curvature radius of the image-side surface of the fourth lens constituting the second optical element group.
12. The imaging lens composed of six optical elements according to claim 2 , wherein the aberration correction optical element is located between the first optical element group and the second optical element group.
13. The imaging lens composed of six optical elements according to claim 2 , wherein the aberration correction optical element is located between the second optical element group and the third optical element group.
14. The imaging lens composed of six optical elements according to claim 2 , wherein the aberration correction optical element is located on the image side of the third optical element group.
15. The imaging lens composed of six optical elements according to claim 2 , wherein conditional expressions (1) and (2) below are satisfied:
0.1< TN/f< 0.5 (1)
40<ν dN< 60 (2)
where
TN: distance on the optical axis of an air gap where the aberration correction optical element is located
f: focal length of an overall optical system of the imaging lens
νdN: Abbe number of the aberration correction optical element at d-ray.
16. The imaging lens composed of six optical elements according to claim 2 , wherein aspheric surfaces on both sides of the aberration correction optical element are shaped so as to curve toward the object side with increasing distance from the optical axis.
17. The imaging lens composed of six optical elements according to claim 2 , wherein a conditional expression (3) below is satisfied:
1.0< fLG 1/ f< 2.0 (3)
where
fLG 1 : focal length of the first optical element group
f: focal length of an overall optical system of the imaging lens.
18. The imaging lens composed of six optical elements according to claim 2 , wherein a conditional expression (4) below is satisfied:
0.3< fLG 2/ f< 1.0 (4)
where
fLG 2 : focal length of the second optical element group
f: focal length of an overall optical system of the imaging lens.
19. The imaging lens composed of six optical elements according to claim 2 , wherein a conditional expression (5) below is satisfied:
−0.8< fLG 3/ f<− 0.2 (5)
where
fLG 3 : focal length of the third optical element group
f: focal length of an overall optical system of the imaging lens.
20. The imaging lens composed of six optical elements according to claim 2 , wherein a conditional expression (6) below is satisfied:
0.8<( r 7+ r 8)/( r 7− r 8)<4.5 (6)
where
r 7 : curvature radius of the object-side surface of the fourth lens constituting the second optical element group
r 8 : curvature radius of the image-side surface of the fourth lens constituting the second optical element group.
21. An imaging lens composed of six optical elements which forms an image of an object on a solid-state image sensor, in which the elements are arranged in order from an object side to an image side, the imaging lens comprising:
a first optical element group with positive refractive power including:
a first lens with positive refractive power having a convex surface on the object side as a first optical element;
a second lens with negative refractive power having a concave surface on the image side as a second optical element; and
a third lens that is a meniscus lens having positive or negative refractive power as a third optical element;
a second optical element group with positive refractive power including a fourth lens with positive refractive power having a convex surface on the image side as a fourth optical element; and
a third optical element group with negative refractive power including a double-sided aspheric fifth lens with negative refractive power having a concave surface on the image side as a fifth optical element, wherein
at least one pole-change point is formed off an optical axis on the image-side surface of the fifth lens; and
a double-sided aspheric aberration correction optical element which has a flat surface near the optical axis with virtually no refractive power as a sixth optical element is located in an air gap nearer to an image plane than the first optical element group.