Optical system and rear projector

• US 20060132723A1
• Filed: 12/09/2005
• Published: 06/22/2006
• Est. Priority Date: 12/13/2004
• Status: Active Grant

• Current Assignee: Nittoh Kogaku Kabushiki Kaisha
• Original Assignee: Nittoh Kogaku Kabushiki Kaisha
• Inventors: Yamagishi, Akira
• Granted Patent: US 7,448,760 B2
• Time in Patent Office: Days
• US Class Current: 353/98
• CPC Class Codes: G03B 21/10 Projectors with built-in or built-on screen
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal

Abstract

An optical system that projects projection light from an image generating device, onto a screen is provided. The optical system comprises: a lens system on which the projection light from the image generating device is incident; and an aspherical mirror with negative power as a whole that is disposed on an optical path between the lens system and the screen, wherein a curvature of the aspherical mirror in the radial direction changes positive to negative on a way from a center to a periphery thereof.

Claims

1. An optical system that projects projection light from an image generating device, onto a screen, the optical system comprising:

a lens system on which the projection light from the image generating device is incident; and

an aspherical mirror with negative power as a whole that is disposed on an optical path between the lens system and the screen, wherein a curvature of the aspherical mirror in the radial direction changes positive to negative on a way from a center to a periphery thereof.

2. The optical system according to claim 1, the curvature of the aspherical mirror decreases from the center to the periphery.

3. The optical system according to claim 1, wherein a lens located at an end of a projection side of the lens system is a meniscus lens that is convex on the projection side.

4. The optical system according to claim 1, wherein the optical system projects the projection light on the screen at an incident angle of at least 45°

.

5. The optical system according to claim 1, wherein a distance D between an aspherical mirror end of the lens system and the aspherical mirror and a combined focal length f of the lens system satisfy a condition below

1.0|f|<

D<

3.0|f|.

6. The optical system according to claim 1, wherein the lens system includes, from a projection side, a front group with negative refractive power, a rear group with positive refractive power, and one of a flat mirror and a prism that bends an optical path between the front group and the rear group.

7. The optical system according to claim 6, wherein the front group includes, from the projection side, a first lens group, which has a negative refractive power and includes at least a meniscus lens that is convex on the projection side, and a second lens group which has a positive refractive power.

8. A projector comprising:

the optical system according to claim 1;

an image generating device; and

a screen entire area thereof being a prism-type Fresnel screen.

9. A rear projector comprising:

the optical system according to claim 1;

an image generating device; and

a screen,

wherein the projection light is projected from a rear side of the screen.

10. The rear projector according to claim 9, wherein entire area of the screen is a prism-type Fresnel screen.