System and image capturing apparatus including the same
A system consists of a front lens unit and a negative lens on an image side of the front lens unit. A focal length of the system, a focal length of the negative lens, an effective diameter of a lens surface on an object side of the negative lens, a diameter of an aperture stop that determines an on-axis ray, and an on-axis distance from an endmost point in a light effective area of the lens surface on the object side of the negative lens to an on-axis point of the negative lens satisfy predetermined inequalities.
1 . A system consisting of a front lens unit and a negative lens Gn on an image side of the front lens unit,
wherein the following inequalities are satisfied:
−10.0< fn/f< −0.7
0.9< D/ST< 1.4
−0.50< SAG 1 /f< −0.16
1.78<NdGp<2.2
where f is a focal length of the system, fn is a focal length of the negative lens Gn, D is an effective diameter of a lens surface on an object side of the negative lens Gn, ST is a diameter of an aperture stop that determines an on-axis ray, SAG 1 is an on-axis distance from an endmost point in a light effective area of the lens surface on the object side of the negative lens Gn to an on-axis point of the negative lens Gn, and NdGp is an average refractive index of positive lenses in the system.
2 . The system according to claim 1 ,
wherein the following inequality is satisfied:
−0.35< −SAG 2 /f< 0
where SAG 2 is an on-axis distance from an endmost point in a light effective area of a lens surface on an image side of the negative lens Gn to an on-axis point of the lens surface on the image side of the negative lens Gn.
3 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.5< GnR 2 /f< 10
where GnR 2 is a radius of curvature of a lens surface on an image side of the negative lens Gn.
4 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.1< Td/f< 2.5
where Td is an on-axis length from a surface vertex of a lens surface closest to the object side in the system to an image plane, where, in Td, a distance from a lens surface closest to the image side to the image plane is an equivalent air length.
5 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0< STd/f< 0.15
where STd is an on-axis distance from a surface vertex on the image side of a lens located adjacent to the aperture stop on the object side to a surface vertex on the object side of a lens located adjacent to the aperture stop on the image side.
6 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.05< skd/SL< 0.15
where skd is an on-axis equivalent air length from a lens surface on an image side of the negative lens Gn to an image plane, SL is an on-axis length from the aperture stop to the image plane, where, in SL, a distance from a lens surface closest to the image side to the image plane is an equivalent air length.
7 . The system according to claim 1 ,
wherein the following inequality is satisfied:
1.45<NdGn<1.70
where NdGn is a refractive index of the negative lens Gn.
8 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.6<gGn<1.7
where gGn is a specific gravity (g/mm 3 ) of a material for the negative lens Gn.
9 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.08<SF1<12.0
where SF 1 is a shape factor of a lens G 1 closest to the object side in the system.
10 . The system according to claim 1 ,
wherein the following inequality is satisfied:
0.6<| f 1 /f 2|<5.0
where f1 is a focal length a lens G 1 closest to the object side in the system, and f2 is a focal length of a second lens G 2 counted from the object side in the system.
11 . The system according to claim 1 , wherein a lens surface on an image side of the negative lens Gn is an aspheric surface having at least one extreme point.
12 . The system according to claim 1 , wherein the front lens unit includes at least six lenses.
13 . The system according to claim 1 , wherein a lens G 1 closest to the object side in the system is a negative lens that is concave on the object side.
14 . The system according to claim 1 ,
wherein the front lens unit includes:
a negative lens closest to the object side;
a positive lens adjacent to an image side of the negative lens; and
a positive lens adjacent to the image side of the positive lens.
15 . An apparatus comprising:
the system according to claim 1 ; and
a sensor that receives an image formed by the system.
16 . The apparatus according to claim 15 ,
wherein the following inequality is satisfied:
−0.35<− SAG 2 /f< 0
where SAG 2 is an on-axis distance from an endmost point in a light effective area of a lens surface on an image side of the negative lens Gn to an on-axis point of the lens surface on the image side of the negative lens Gn.
17 . The apparatus according to claim 15 ,
wherein the following inequality is satisfied:
0.5< GnR 2 /f< 10
where GnR 2 is a radius of curvature of a lens surface on an image side of the negative lens Gn.
18 . The apparatus according to claim 15 ,
wherein the following inequality is satisfied:
0.1< Td/f< 2.5
where Td is an on-axis equivalent air length from a surface vertex of a lens surface closest to the object side in the system to an image plane.
19 . The apparatus according to claim 15 ,
wherein the following inequality is satisfied:
0< STd/f< 0.15
where STd is an interval between surface vertexes of lenses in front of and behind the aperture stop.