Image projector

• US 7,677,738 B2
• Filed: 04/06/2005
• Issued: 03/16/2010
• Est. Priority Date: 04/27/2004
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Kuwata, Muneharu, Kojima, Kuniko, Yamada, Akihiro, Sasagawa, Tomohiro
• Primary Examiner(s): Epps; Georgia Y
• Assistant Examiner(s): HOWARD, RYAN D
• Application Number:
  US11/587,699
• Publication Number:
  US 20070229779A1
• Time in Patent Office: 1,805 Days
• Field of Search: 353/77, 353/78, 353/98, 353/99, 353/100, 359/649, 359/650, 359/651
• US Class Current: 353/78
• CPC Class Codes: G02B 13/16 for use in conjunction with image converters or intensifiers , or for use with projectors, e.g. objectives for projection TV
• CPC Class Codes: G02B 17/08 Catadioptric systems used in non-imaging applications G02B19/00
• CPC Class Codes: G02B 17/0852 having a field corrector only
• 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 5/7408 Direct viewing projectors, e.g. an image displayed on a video CRT or LCD display being projected on a screen
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

According to the present invention, an image projector includes a reflecting light valve, a group of refracting lenses forming a projecting optical system that enlarges and projects an optical image given from the light valve, a power mirror having a power and forming the projecting optical system together with the group of refracting lenses, and a transmissive screen for displaying the optical image that is given from the light valve and enlarged by the projecting optical system, wherein the exit pupil position is set such that the minimum angle of view θmin exceeds 40°, and the Petzval partial sum of lenses is set larger than a value determined by the minimum angle of view.

Claims

1. An image projector comprising:

a reflecting light valve that displays an optical image;

a projecting optical system that enlarges and projects said optical image given from said light valve; and

a screen onto which said optical image enlarged by said projecting optical system is projected,

said projecting optical system comprising;

a group of refracting lenses that receives and enlarges light from said light valve; and

a power mirror that has a power and that receives, and enlarges and reflects light from said group of refracting lenses,

wherein a display surface of said light valve and a screen surface of said screen are disposed perpendicular to an optical axis,

and wherein, when a minimum value of an angle formed between a normal to said screen surface and principal rays incident upon said screen is a minimum angle of view θ

min, and,

about said group of refracting lenses,

a radius of curvature of an ith surface is r_i,

a refractive index of said ith surface is n_i,

a refractive index of an (i+1)th surface is n_i+1, and

a total number of lens surfaces is N,

and a sum of Petzval components of the surfaces of the plurality of lenses of said group of refracting lenses is a Petzval partial sum of the lenses, PL, and

PL=Σ

{−

1/r_i×

(1/n_i+1−

1/n_i)} [i=1, . . . , N],

then, in said projecting optical system,

an exit pupil position is set such that said minimum angle of view θ

min exceeds 40°

, and a relation of PL>

0.0007×

θ

min−

0.026 is satisfied.

2. The image projector according to claim 1, wherein the optical image enlarged by said projecting optical system is projected directly from said power mirror onto said screen.

3. The image projector according to claim 1,

wherein said group of refracting lenses is positioned on a side of said power mirror in a horizontal direction,

said projecting optical system further comprises a plane mirror that is positioned optically between said group of refracting lenses and said power mirror, said plane mirror having no power and bending said optical axis toward said power mirror in a horizontal plane, and

said plane mirror is disposed to bend said optical axis at an angle ±

1 that satisfies a condition expressed by Expression below

46°

≦

β

1≦

60°

.

4. The image projector according to claim 3,

wherein, when a horizontal distance from a surface vertex of said power mirror to a position right under said screen is L1, and

a distance along said optical axis between the surface vertex of said power mirror and a surface vertex of a lens placed closest to said screen in said group of refracting lenses is L2,

then, said projecting optical system is disposed to satisfy a condition expressed by Expression below

0.4<

L1/L2<

0.9.

5. The image projector according to claim 1,

wherein said group of refracting lenses is positioned vertically under said power mirror such that said optical axis is parallel to the normal to said screen surface,

said projecting optical system comprises first and second plane mirrors that are positioned optically between said group of refracting lenses and said power mirror, said first and second plane mirrors having no power and bending said optical axis respectively at an angle α

1 and an angle α

2 in a vertical direction and a horizontal direction so as to bend said optical axis at 180°

in a vertical plane, and

said first plane mirror is disposed such that said angle α

1 at which said optical axis is bent satisfies a condition expressed by Expression below

100°

≦

α

1≦

140°

.

6. The image projector according to claim 5,

wherein, when a horizontal distance from a surface vertex of said power mirror to a position right under said screen is L1, and

a distance along said optical axis between the surface vertex of said power mirror and a surface vertex of a lens placed closest to said screen in said group of refracting lenses is L2,

then, said projecting optical system is disposed to satisfy a condition expressed by Expression below

0.4<

L1/L2<

0.9.

7. The image projector according to claim 1,

wherein said projecting optical system comprises:

a plane mirror that is positioned optically between said group of refracting lenses and said power mirror, said plane mirror having no power and bending said optical axis in a horizontal plane; and

a rear mirror that is positioned geometrically behind said screen in parallel with said screen surface, and optically between said power mirror and said screen, said rear mirror bending said optical axis at 180°

in a vertical plane,

and wherein said group of refracting lenses is positioned on a side of said power mirror in a horizontal direction, and positioned between said screen and said rear mirror when said screen and said rear mirror are imaginarily extended downward, and

said plane mirror is disposed to bend said optical axis at an angle β

2 that satisfies a condition expressed by Expression below

46°

≦

β

2≦

90°

.

8. The image projector according to claim 7,

wherein, when a difference between a maximum value and a minimum value of an angle formed between said optical axis and a group of principal rays emitted from said power mirror is θ

, and

a difference between a maximum value and a minimum value of an angle formed between said optical axis and a group of principal rays emitted from said group of refracting lenses is ω

,

then, said θ and

said ω

satisfy a relation expressed by Expression below

θ

/ω

<

1.

9. The image projector according to claim 1,

wherein said projecting optical system comprises:

a plane mirror that is positioned optically between said group of refracting lenses and said power mirror, said plane mirror having no power and bending said optical axis in a vertical plane; and

a rear mirror that is positioned geometrically behind said screen in parallel with said screen surface, and optically between said power mirror and said screen, said rear mirror bending said optical axis at 180°

in a vertical plane,

and wherein said group of refracting lenses is positioned vertically under said power mirror such that said optical axis has a tilt with respect to the normal to the screen surface, and positioned between said screen and said rear mirror when said screen and said rear mirror are imaginarily extended downward, and

said plane mirror is disposed to bend said optical axis at an angle α

3 that satisfies a condition expressed by Expression below

40°

≦

α

3≦

50°

.

10. The image projector according to claim 9,

wherein, when a difference between a maximum value and a minimum value of an angle formed between said optical axis and a group of principal rays emitted from said power mirror is θ

, and

a difference between a maximum value and a minimum value of an angle formed between said optical axis and a group of principal rays emitted from said group of refracting lenses is ω

,

then, said θ and

said ω

satisfy a relation expressed by Expression below

θ

/ω

<

1.

11. The image projector according to claim 1, wherein said light valve has its center offset vertically downward from said optical axis of said projecting optical system.

12. The image projector according to claim 1, wherein said screen is a transmissive screen formed of a total-reflecting Fresnel lens.