Projection-type display apparatus

• US 20050018148A1
• Filed: 07/06/2004
• Published: 01/27/2005
• Est. Priority Date: 07/22/2003
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Hasegawa, Masahide
• Granted Patent: US 7,281,805 B2
• Time in Patent Office: Days
• US Class Current: 353/98
• CPC Class Codes: G02B 27/0018 with means for preventing ghost images anti-reflection coatings G02B1/11
• CPC Class Codes: G02B 27/18 for optical projection, e.g. combination of mirror and condenser and objective photographic, cine and overhead projectors G03B21/00; photographic projection printing G03B27/32; photolithographic projectors G03F7/20; projection television H04N5/74; colour projection television H04N9/31
• CPC Class Codes: G03B 21/10 Projectors with built-in or built-on screen
• CPC Class Codes: H04N 5/72 Modifying the appearance of television pictures by optical filters or diffusing screens
• CPC Class Codes: H04N 5/7408 Direct viewing projectors, e.g. an image displayed on a video CRT or LCD display being projected on a screen
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal
• CPC Class Codes: H04N 9/3141 Constructional details thereof details not peculiar to the presence of an electronic spatial light modulator G03B21/14

Abstract

A thin-shaped projection-type display apparatus capable of displaying a high-quality image without causing any ghost image is provided. The projection-type display apparatus includes a screen having a prism, and a projection optical system for guiding image light to the screen. The projection optical system includes a plurality of optical elements. An optical element disposed nearest to the screen on an optical path of the image light among the plurality of optical elements is a mirror. An angle made by the normal to a surface of the mirror approximately at the center of the mirror and the normal to a surface of the screen is between 75 degrees and 87.5 degrees inclusive.

Claims

1. A projection-type display apparatus, comprising:

a screen having a prism; and

a projection optical system for guiding image light to the screen, the projection optical system including a plurality of optical elements,

wherein an optical element disposed nearest to the screen on an optical path of the image light among the plurality of optical elements is a mirror, and

wherein an angle made by a normal to a surface of the mirror approximately at the center of the mirror and a normal to a surface of the screen is between 75 degrees and 87.5 degrees inclusive.

2. A projection-type display apparatus, comprising:

a projection optical system for guiding image light to a screen, the projection optical system including a plurality of optical elements,

wherein an optical element disposed nearest to the screen on an optical path of the image light among the plurality of optical elements is a mirror,

wherein an angle a made by an optical path of the image light falling on the screen after passing through the center of a pupil of the projection optical system and a normal to a surface of the screen is between 60 degrees and 85 degrees inclusive, and

wherein an angle made by a normal to a surface of the mirror approximately at the center of the mirror and the normal to the surface of the screen is between (45+(a minimum value of the angle a)/2) degrees and (45+(a maximum value of the angle a)/2) degrees inclusive.

3. A projection-type display apparatus according to claim 2, wherein the angle a made by an optical path of the image light falling on the screen after passing through the center of a pupil of the projection optical system and a normal to a surface of the screen is 65 degrees or more.

4. A projection-type display apparatus according to claim 2, wherein the angle a made by an optical path of the image light falling on the screen after passing through the center of a pupil of the projection optical system and a normal to a surface of the screen is 80 degrees or less.

5. A projection-type display apparatus according to claim 2, wherein the screen has a prism, the prism having an approximately triangular shape having an apex angle ?t facing the mirror, the apex angle ?t being between 50 degrees and 65 degrees inclusive.

6. A projection-type display apparatus according to claim 5, wherein the apex angle ?t is 55 degrees or more.

7. A projection-type display apparatus according to claim 5, wherein the apex angle ?t is 61 degrees or less.

8. A projection-type display apparatus, comprising:

a total-reflection-prism-type Fresnel lens including an array of concentrically arranged prisms, each prism having a total-reflection surface;

a screen allowing image light to be incident on a back side thereof and to be viewable on a front side thereof by a viewer;

a projection optical system for projecting the image light obliquely onto a surface of the screen; and

at least one plane mirror disposed between the projection optical system and the screen,

wherein an incident angle a of a ray incident on the screen from the projection optical system is between 60 degrees and 85 degrees inclusive, and

wherein an angle ? made by a normal to a surface of a mirror nearest to the screen among the at least one plane mirror and a normal to the surface of the screen satisfies the following condition;

(45+(a minimum value of the angle a)/2) degrees=?=(45+(a maximum value of the angle a)/2) degrees.

9. A projection-type display apparatus according to claim 8, wherein an apex angle ?t of each prism is set to such an angle as to prevent a ray reflecting from an entrance surface of the prism and reflecting from the plane mirror nearest to the screen from falling again on the screen.

10. A projection-type display apparatus according to claim 8, wherein the apex angle ?t is constant with respect to all the prisms, and an angle ?s of an entrance surface of each prism with the surface of the screen is varied according to the incident angle a of a ray incident on the screen so as to make a ray emerging from the prism perpendicular to the screen.