Image capturing lens and image capturing apparatus
View Patent ↗Arranging a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a negative fifth lens from the object side, in which the image side surface of the fifth lens has an aspherical shape with one or more inflection points and a concave shape toward the image side in a paraxial region, and, when the focal length of the entire lens system, radius of curvature of the image side surface of the first lens, radius of curvature of the image side surface of the second lens, overall optical length, focal length of j th lens, and Abbe number of j th lens are taken as f, R2, R4, TL, fj, and νj respectively, the image capturing lens is configured to simultaneously satisfy conditional expressions (1a): −1.5<f/R2<1.6, (2a): −1.6<f/R4<0.05, (3a): 0.95≦f4/f≦4.3, (5a): 1.0≦TL/f≦2.2, and (12b): −2.0<Σ(fj/νj)/f<0.5.
1. An image capturing lens substantially consisting of a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power, arranged in this order from the object side, wherein:
the image side surface of the fifth lens has an aspherical shape with one or more inflection points and a concave shape toward the image side in a paraxial region; and
the image capturing lens satisfies the following conditional expressions (1a), (2a), (3a), (5a), and (12b) simultaneously:
−1.5 <f/R 2<1.6 (1a);
−1.6 <f/R 4<0.05 (2a);
0.95 ≦f 4 /f≦ 4.3 (3a),
1.0 ≦TL/f≦ 2.2 (5a); and
−2.0<Σ( fj/νj )/ f< 0.5 (12b),
where:
f is a focal length of the entire lens system;
R2 is a radius of curvature of the image side surface of the first lens;
R4 is a radius of curvature of the image side surface of the second lens;
f4 is a focal length of the fourth lens;
TL is an overall optical length when a distance from the image side surface of the fifth lens to the image plane is represented by an air equivalent length;
Σ(fj/νj)/f is [(f1/ν1)+(f2/ν2)+(f3/ν3)+(f4/ν4)+(f5/ν5)]/f;
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;
f5 is a focal length of the fifth lens;
ν1 is an Abbe number of the first lens;
ν2 is an Abbe number of the second lens;
ν3 is an Abbe number of the third lens;
ν4 is an Abbe number of the fourth lens; and
ν5 is an Abbe number of the fifth lens.
2. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (4a):
0.55 ≦f 12 /f≦ 5.0 (4a),
where f12 is a combined focal length of the first and second lenses.
3. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (6a):
0.1 ≦Bf/f≦ 0.5 (6a),
where Bf is a back focus when a distance from the image side surface of the fifth lens to the image plane is represented by an air equivalent length.
4. The image capturing lens of claim 1 , wherein the image side surface of the fourth lens is a convex or planar surface in a paraxial region.
5. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (7a):
−12<( R 1 +R 2)/( R 1 −R 2)<−0.21 (7a),
where:
R1 is a radius of curvature of the object side surface of the first lens (first lens surface); and
R2 is a radius of curvature of the image side surface of the first lens (second lens surface).
6. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (8a):
18<ν1<50 (8a),
where ν1 is an Abbe number of the first lens.
7. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (9a):
0.25<( Dg 2 +Dg 3)/ f< 0.7 (9a),
where:
Dg 2 is an axial thickness of the second lens (a distance between the object side surface and image side surface of the second lens on the optical axis; actual length); and
Dg 3 is an axial thickness of the third lens (a distance between the object side surface and image side surface of the third lens on the optical axis; actual length).
8. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (10a):
50<ν4<65 (10a),
where ν4 is an Abbe number of the fourth lens.
9. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (12a):
−4.0<Σ( fj/νj )/ f< 4.0 (12a),
where Σ(fj/νj)/f is [(f1/ν1)+(f2/ν2)+(f3/ν3)+(f4/ν4)+(f5/ν5)]/f.
10. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (1b):
−1.0 <f/R 2<1.6 (1b).
11. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (2b):
−1.4 <f/R 4<0.05 (2b).
12. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (3b):
0.95 ≦f 4 /f≦ 2.1 (3b).
13. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (4b):
0.60 ≦f 12 /f≦ 1.30 (4b),
where f12 is a combined focal length of the first and second lenses.
14. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (4c):
0.65 ≦f 12 /f≦ 1.30 (4c),
where f12 is a combined focal length of the first and second lenses.
15. The image capturing lens of claim 1 , wherein the lens satisfies the following conditional expression (9b):
0.45<( Dg 2 +Dg 3)/ f< 0.6 (9b),
where:
Dg 2 is an axial thickness of the second lens (a distance between the object side surface and image side surface of the second lens on the optical axis; actual length); and
Dg 3 is an axial thickness of the third lens (a distance between the object side surface and image side surface of the third lens on the optical axis; actual length).
16. An image capturing apparatus, comprising the image capturing lens of claim 1 .