Optical system and image pickup apparatus including the same
An optical system includes an aperture stop, and a focus lens unit arranged on an image side of the aperture stop, the focus lens unit having a negative refractive power and moving during focusing. The focus lens unit moves toward the image side during focusing from infinity to close distance. The focus lens unit includes a positive lens PL and a negative lens NL. An Abbe number νdNL of the material of the negative lens NL, a refractive index NdNL of the material of the negative lens NL at d-line, and an Abbe number νdPL of the material of the positive lens PL are set appropriately.
1. An optical system comprising:
an aperture stop; and
a focus lens unit arranged on an image side of the aperture stop, the focus lens unit having a negative refractive power and moving during focusing, wherein
the focus lens unit moves toward the image side during focusing from infinity to close distance and includes a positive lens PL and a negative lens NL, and
the following conditional expressions are satisfied:
23.0<ν dNL< 40.0;
2.44< NdNL− 0.0003×ν dNL 2 +0.034×ν dNL< 2.64; and
ν dPL< 23.0,
where νdNL denotes an Abbe number of a material of the negative lens NL, NdNL denotes a refractive index of the material of the negative lens NL at d-line, and νdPL denotes an Abbe number of a material of the positive lens PL.
2. The optical system according to claim 1 , wherein
provided that νd denotes an Abbe number of a material, θgF denotes a partial dispersion ratio of the material based on g-line and F-line, and θgFa denotes a standard partial dispersion ratio and is defined as
θ gFa=− 1.665×10 −7 ×νd 3 +5.213×10 −5 ×νd 2 −5.656×10 −3 ×νd+ 0.7268,
the following conditional expression is satisfied,
θ gFNL<θgFaNL,
where θgFNL denotes a partial dispersion ratio of the material of the negative lens NL based on the g-line and the F-line, and θgFaNL denotes a standard partial dispersion ratio of the material of the negative lens NL.
3. The optical system according to claim 1 , wherein
provided that vd denotes an Abbe number of a material, θgF denotes a partial dispersion ratio of the material based on g-line and F-line, and θgFa denotes a standard partial dispersion ratio and is defined as
θ gFa=− 1.665×10 −7 ×νd 3 +5.213×10 −5 ×νd 2 −5.656×10 −3 ×νd+ 0.7268,
the following conditional expression is satisfied,
θ gFaPL<θgFPL,
where θgFPL denotes a partial dispersion ratio of the material of the positive lens PL based on the g-line and the F-line, and θgFaPL denotes a standard partial dispersion ratio of the material of the positive lens PL.
4. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
DNL<− 3.1× NdNL 2 +14.7× NdNL− 12.5,
where DNL denotes a specific gravity of the material of the negative lens NL.
5. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
DPL<− 3.1× NdPL 2 +14.7× NdPL− 12.5,
where NdPL denotes a refractive index of the material of the positive lens PL at the d-line, and DPL denotes a specific gravity of the material of the positive lens PL.
6. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
1.80< NdPL,
where NdPL denotes a refractive index of the material of the positive lens PL at the d-line.
7. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
DNL< 3.70,
where DNL denotes a specific gravity of the material of the negative lens NL.
8. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
DPL< 3.70,
where DPL denotes a specific gravity of the material of the positive lens PL.
9. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
1.2<ν dNL/νdPL< 2.2.
10. The optical system according to claim 1 , wherein
the following conditional expression is satisfied,
0.0<( R 1 NL+R 2 NL )/( R 1 NL−R 2 NL )<1.0,
where R1NL denotes a radius of curvature of an object-side lens surface of the negative lens NL and R2NL denotes a radius of curvature of an image-side lens surface of the negative lens NL.
11. The optical system according to claim 1 , wherein
the focus lens unit consists of the positive lens PL and the negative lens NL.
12. The optical system according to claim 1 , wherein
the optical system consists, in order from an object side to the image side, of a first lens unit having a positive refractive power, the aperture stop, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power, and
the second lens unit is the focus lens unit and moves during focusing.
13. The optical system according to claim 1 , wherein
the optical system consists, in order from an object side to the image side, of a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, the aperture stop, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, a fifth lens unit having a positive refractive power, a sixth lens unit having a negative refractive power, a seventh lens unit having a negative refractive power, and an eighth lens unit having a positive refractive power,
a distance between each pair of neighboring ones of the lens units changes during zooming, and
the sixth lens unit is the focus lens unit that moves during focusing.
14. The optical system according to claim 1 , wherein
the optical system consists, in order from an object side to the image side, of a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, the aperture stop, a fourth lens unit having a positive refractive power, a fifth lens unit having a negative refractive power, and a sixth lens unit having a positive refractive power,
a distance between each pair of neighboring ones of the lens units changes during zooming, and
the fifth lens unit is the focus lens unit that moves during focusing.
15. The optical system according to claim 1 , wherein
the optical system consists, in order from an object side to the image side, of a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,
a distance between each pair of neighboring ones of the lens units changes during zooming,
the aperture stop is arranged inside the second lens unit, and
the third lens unit is the focus lens unit that moves during focusing.
16. An image pickup apparatus comprising:
an optical system; and
an image pickup element which receives a light image formed by the optical system,
wherein the optical system includes an aperture stop, and a focus lens unit arranged on an image side of the aperture stop, the focus lens unit having a negative refractive power and moving during focusing,
the focus lens unit moves toward the image side during focusing from infinity to close distance, and includes a positive lens PL and a negative lens NL, and
the following conditional expressions are satisfied:
23.0<ν dNL< 40.0;
2.44< NdNL− 0.0003×ν dNL 2 +0.034×ν dNL< 2.64; and
ν dPL< 23.0,
where νdNL denotes an Abbe number of a material of the negative lens NL, NdNL denotes a refractive index of the material of the negative lens NL at d-line, and νdPL denotes an Abbe number of a material of the positive lens PL.