Projection optical system
AssigneeNissei Technology Corporation
InventorTakuya Otsu
Life of this patent
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Abstract
A projection optical system includes, in sequence from a projection surface: an aperture stop; a first lens with a positive refractive power; a second lens with a positive refractive power; and a third lens with a positive refractive power. The third lens have a convex surface closer to the projection surface. The projection system satisfies: 1.0<f/EPD<1.35, 1.0<(r2+r1)/(r2−r1)<1.45, and 0.2<d2/f<0.45, where f is a focal length of the overall projection optical system, EPD is an entrance pupil diameter, r1 is a radius of curvature of a surface of the first lens closer to the projection surface, r2 is a radius of curvature of a surface of the first lens closer to the image display element, and d2 is an air spacing between the first lens and the second lens on an optical axis.
Claims2
A projection optical system for projecting an image from an image display element in a magnified manner onto a projection surface, the system comprising, in sequence from the projection surface:
- an aperture stop;
- a first lens with a positive refractive power;
- a second lens with a positive refractive power;
- and
- a third lens with a positive refractive power, the third lens having a convex surface facing the projection surface side,
- wherein the projection optical system satisfies the conditional expressions:
- 1.
- <
- f
- /
- EPD
- <
- 1.35
- (
- 1
- )
- 1.
- <
- (
- r
-
- 2
- +
- r
-
- 1
- )
- /
- (
- r
-
- 2
- -
- r
-
- 1
- )
- <
- 1.45
- (
- 2
- )
- 0.2
- <
- d
-
- 2
- /
- f
- <
- 0.45
- (
- 3
- )
- where f is a focal length of the overall projection optical system,
- EPD is an entrance pupil diameter,
- r1 is a radius of curvature of a projection surface side of the first lens surface,
- r2 is a radius of curvature of an image display element side of the first lens surface, and
- d2 is an air spacing between the first lens and the second lens on an optical axis.
Dependencies are inferred from the claim text.