Optical system, optical apparatus, and image pickup apparatus
An optical system includes a first unit fixed during focusing, a second unit configured to move during focusing, and a third unit fixed during focusing on an image side of the second unit. The first unit includes a first optical element having a first reflective surface that has a concave shape toward an object side, and a second optical element having a second reflective surface that has a convex shape toward an image side. Light incident on the optical system from an object is reflected by the first reflective surface, thereafter is reflected by the second reflective surface, and thereafter passes through the second unit. A predetermined inequality is satisfied.
1 . An optical system comprising:
a first unit fixed during focusing;
a second unit configured to move during focusing; and
a third unit fixed during focusing on an image side of the second unit,
wherein the first unit includes:
a first optical element having a first reflective surface that has a concave shape toward an object side; and
a second optical element having a second reflective surface that has a convex shape toward the image side,
wherein the second unit includes a negative lens having a concave shape toward the image side,
wherein light incident on the optical system from an object is reflected by the first reflective surface, thereafter is reflected by the second reflective surface, and thereafter passes through the second unit, and
wherein the following inequalities are satisfied:
nM1 ≤1.690
0.440≤L/f≤0.800
where nM1 is a refractive index of the first optical element for d-line, L is a distance on an optical axis from a surface closest to the object of the optical system to the image plane, and f is a focal length of the optical system.
2 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.720≤rR1/rR2≤1.450
where rR1 is a radius of curvature of the first reflective surface, and rR2 is a radius of curvature of the second reflective surface.
3 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.340≤|dM1M2|/dM1IP≤0.720
where dM1M2 is a distance on the optical axis between the first reflective surface and the second reflective surface, and dM1IP is a distance on the optical axis from the first reflective surface to the image plane.
4 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.380≤eamax/L≤1.000
where eamax is an effective diameter of an optical surface having the largest effective diameter among optical surfaces included in the optical system.
5 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.500≤dM1IP/L<1.000
where dM1IP is a distance on the optical axis from the first reflective surface to the image plane.
6 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.1290≤|dM1M2|/f ≤0.2500
where dM1M2 is a distance on the optical axis between the first reflective surface and the second reflective surface.
7 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.0010≤βL2/f≤0.0500
where βL2 is a lateral magnification of the second unit in an in-focus state at infinity.
8 . The optical system according to claim 1 , wherein the following inequality is satisfied:
−1.200≤rR1/f≤−0.450
where rR1 is a radius of curvature of the first reflective surface.
9 . The optical system according to claim 1 , wherein the following inequality is satisfied:
−1.200≤rR2/f≤−0.350
where rR2 is a radius of curvature of the second reflective surface.
10 . The optical system according to claim 1 , wherein the following inequality is satisfied:
0.020≤tmax/L≤0.075
where tmax is a thickness of a lens having the largest thickness on the optical axis among lenses included in the optical system.
11 . The optical system according to claim 1 , wherein the first unit includes a positive lens which the light from the object first enters.
12 . The optical system according to claim 1 , wherein the third unit includes a positive lens and a negative lens.
13 . The optical system according to claim 1 , wherein the first unit includes a lens subunit transmits light traveling from the second reflective surface to the second unit, and
wherein the lens subunit includes a positive lens.
14 . The optical system according to claim 1 , wherein the following inequality is satisfied:
1.000≤nM1≤1.690.
15 . An optical apparatus comprising:
an optical system; and
a holding member configured to hold the optical system,
wherein the optical system includes
a first unit fixed during focusing;
a second unit configured to move during focusing; and
a third unit fixed during focusing on an image side of the second unit,
wherein the first unit includes:
a first optical element having a first reflective surface that has a concave shape toward an object side; and
a second optical element having a second reflective surface that has a convex shape toward the image side,
wherein the second unit includes a negative lens having a concave shape toward the image side,
wherein light incident on the optical system from an object is reflected by the first reflective surface, thereafter is reflected by the second reflective surface, and thereafter passes through the second unit, and
wherein the following inequalities are satisfied:
nM1≤1.690
0.440≤L/f≤0.800
where nM1 is a refractive index of the first optical element for d-line, L is a distance on an optical axis from a surface closest to the object of the optical system to the image plane, and f is a focal length of the optical system.
16 . The optical apparatus according to claim 15 , wherein the following inequality is satisfied:
1.000≤nM1≤1.690.
17 . An image pickup apparatus comprising:
an optical system; and
an image sensor configured to image an object via the optical system,
a first unit fixed during focusing;
a second unit configured to move during focusing; and
a third unit fixed during focusing on an image side of the second unit,
wherein the first unit includes:
a first optical element having a first reflective surface that has a concave shape toward an object side; and
a second optical element having a second reflective surface that has a convex shape toward the image side,
wherein the second unit includes a negative lens having a concave shape toward the image side,
wherein light incident on the optical system from an object is reflected by the first reflective surface, thereafter is reflected by the second reflective surface, and thereafter passes through the second unit, and
wherein the following inequalities are satisfied:
nM1 ≤1.690
0.440≤L/f≤ 0 . 800
where nM1 is a refractive index of the first optical element for d-line, L is a distance on an optical axis from a surface closest to the object of the optical system to the image plane, and f is a focal length of the optical system.
18 . The image pickup apparatus according to claim 17 , wherein the following inequality is satisfied:
1.000≤nM1≤1.690.