Observation optical system and observation apparatus including the same
Provided is an observation optical system used for observing an image displayed on an image display surface. The observation optical system includes, in order from an observation surface side to the image display surface side, a first lens having a positive refractive power, and a second lens having a positive refractive power. The first lens is a Fresnel lens, and a focal length f1 of the first lens and a focal length f2 of the second lens are each appropriately set.
1. An observation optical system used for observing an image displayed on an image display surface, the observation optical system comprising, in order from an observation surface side to the image display surface side:
a first lens having a positive refractive power; and
a second lens having a positive refractive power and disposed on the image display surface side of the first lens,
wherein the first lens is a Fresnel lens, and
wherein the following conditional expression is satisfied:
1.50< f 1/ f 2<2.75; and
0.01< L/f< 0.080,
where f1 is a focal length of the first lens, f2 is a focal length of the second lens, f is a focal length of the observation optical system, and L is a distance from a lens surface on the observation surface side of a lens that is located closest to the observation surface side to a lens surface on the image display surface side of the first lens.
2. An observation optical system according to claim 1 , wherein the first lens has a surface on the image display surface side that is a Fresnel surface.
3. An observation optical system according to claim 1 , wherein the first lens has a surface on the observation surface side that has a continuous shape in a ray effective area.
4. An observation optical system according to claim 1 , wherein the following conditional expression is satisfied:
50.0< h 1/λ d< 500.0,
where h 1 is a length in an optical axis direction of a grating wall surface of a first ring adjacent to a center ring of a Fresnel surface of the first lens, and λd is a length of a wavelength of a d-line.
5. An observation optical system according to claim 1 , wherein the following conditional expression is satisfied:
−1.5<( R 12+ R 11)/( R 12− R 11)<−0.8,
where R 11 is a curvature radius of a surface on the observation surface side of the first lens, and R 12 is a curvature radius of a surface on the image display surface side of the first lens.
6. An observation optical system according to claim 1 , wherein the following conditional expression is satisfied:
−1.5<( R 22+ R 21)/( R 22− R 21)<−0.6,
where R 21 is a curvature radius of a surface on the observation surface side of the second lens, and R 22 is a curvature radius of a surface on the image display surface side of the second lens.
7. An observation optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.20< d/f< 0.45,
where d is a distance from a surface on the observation surface side of the first lens to a surface on the image display surface side of the second lens.
8. An observation apparatus, comprising:
an image display element, which is configured to display image information; and
an observation optical system used for observing an image displayed on an image display surface of the image display element,
wherein the observation optical system includes, in order from an observation surface side to the image display surface side:
a first lens having a positive refractive power; and
a second lens having a positive refractive power and disposed on the image display surface side of the first lens,
wherein the first lens is a Fresnel lens, and
wherein the following conditional expression is satisfied:
1.50< f 1/ f 2<2.75; and
0.01< L/f< 0.080,
where f1 is a focal length of the first lens, f2 is a focal length of the second lens, f is a focal length of the observation optical system, and L is a distance from a lens surface on the observation surface side of a lens that is located closest to the observation surface side to a lens surface on the image display surface side of the first lens.
9. An observation apparatus according to claim 8 , wherein the following conditional expression is satisfied:
0.5< y /Lall<0.8,
where y is an actual image height of the image display surface at an eye relief of 10 mm and a half angle of view of 45°, and Lall is a distance from the observation surface to the image display surface at the eye relief of 10 mm.
10. An observation apparatus according to claim 8 , wherein the following conditional expression is satisfied:
−0.30<( y−y 0)/ y 0<−0.15,
where y 0 is an ideal image height of the image display surface at an eye relief of 10 mm and a half angle of view of 45°, and y is an actual image height of the image display surface at the eye relief of 10 mm and the half angle of view of 45°.
11. An observation optical system according to claim 1 , wherein the following conditional expression is satisfied:
50.0< h 1/λ d< 400.0,
where h 1 is a length in an optical axis direction of a grating wall surface of a first ring adjacent to a center ring of a Fresnel surface of the first lens, and λd is a length of a wavelength of a d-line.
12. An observation apparatus according to claim 8 , wherein the following conditional expression is satisfied:
−0.25<( y−y 0)/ y 0<−0.15,
where y 0 is an ideal image height of the image display surface at an eye relief of 10 mm and a half angle of view of 45°, and y is an actual image height of the image display surface at the eye relief of 10 mm and the half angle of view of 45°.
13. An observation apparatus, comprising:
an image display element, which is configured to display image information; and
an observation optical system used for observing an image displayed on an image display surface of the image display element,
wherein the observation optical system includes, in order from an observation surface side to the image display surface side:
a first lens having a positive refractive power; and
a second lens having a positive refractive power,
wherein the first lens is a Fresnel lens, and
wherein the following conditional expression is satisfied:
1.50< f 1/ f 2<2.75; and
−0.30<( y−y 0)/ y 0<−0.15,
where f1 is a focal length of the first lens, f2 is a focal length of the second lens, y 0 is an ideal image height of the image display surface at an eye relief of 10 mm and a half angle of view of 45°, and y is an actual image height of the image display surface at the eye relief of 10 mm and the half angle of view of 45°.
14. An observation apparatus according to claim 13 , wherein the following conditional expression is satisfied:
—0.25<( y−y 0)/ y 0<−0.15.