Rear projector

• US 20080158518A1
• Filed: 12/26/2007
• Published: 07/03/2008
• Est. Priority Date: 12/27/2006
• Status: Active Grant

• Current Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Inventors: Imaoka, Masayuki, Ishihara, Jun
• Granted Patent: US 7,950,806 B2
• Time in Patent Office: Days
• US Class Current: 353/70
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066
• CPC Class Codes: G03B 21/62 Translucent screens

Abstract

A rear projector for performing image projection includes: a screen and a projection optical system. The screen has a rotationally symmetric Fresnel lens. The projection optical system has at least one reflection surface formed of a rotationally asymmetric free curved surface. The projection optical system is nonaxisymmetric and makes a central principle ray incident obliquely on the screen in the image projection. The Fresnel lens has aberration that cancels out pupil aberration of the projection optical system so that principal rays of beams exiting from the Fresnel lens become substantially parallel to each other.

Claims

1. A rear projector for performing image projection, comprising:

a screen including a rotationally symmetric Fresnel lens; and

a projection optical system being nonaxisymmetric and making a central principle ray incident obliquely on the screen in the image projection, the projection optical system having at least one reflection surface formed of a rotationally asymmetric free curved surface;

wherein the Fresnel lens has aberration that cancels out pupil aberration of the projection optical system so that principal rays of beams exiting from the Fresnel lens become substantially parallel to each other.

2. The rear projector according to claim 1,

wherein the projection optical system is a nonaxisymmetric projection optical system that does not form an intermediate image, and

wherein when, within a plane including a central principal ray immediately before reaching the screen and a normal line of the screen at a point which the ray reaches, an intersection of the central principal ray and the screen is O, an intersection of an extension line La, from a screen direction, of a principal ray of a beam incident on the screen at a largest angle of incidence and an extension line Lb, from the screen direction, of a principal ray of a beam incident on the screen at a smallest angle of incidence is P, an intersection of a perpendicular line drawn from the intersection P to an extension surface of a screen surface and the extension surface of the screen surface is Q, and an amount of offset of the Fresnel lens (distance from a screen center to a rotation symmetry center of the Fresnel lens) is FO, then conditional formula (1) below is satisfied:

FO<

OQ 

 

(1).

3. The rear projector according to claim 1,

wherein the projection optical system is a nonaxisymmetric projection optical system that forms an intermediate image, and

wherein when, within a plane including a central principal ray immediately before reaching the screen and a normal line of the screen at a point which the ray reaches, an intersection of the central principal ray and the screen is O, an intersection of an extension line La, from a screen direction, of a principal ray of a beam incident on the screen at a largest angle of incidence and an extension line Lb, from the screen direction, of a principal ray of a beam incident on the screen at a smallest angle of incidence is P, an intersection of a perpendicular line drawn from the intersection P to an extension surface of a screen surface and the extension surface of the screen surface is Q, and an amount of offset of the Fresnel lens (distance from a screen center to a rotation symmetry center of the Fresnel lens) is FO, then conditional formula (2) below is satisfied:

OQ<

FO 

 

(2).

4. The rear projector according to claim 1,

wherein the projection optical system is a nonaxisymmetric projection optical system that does not form an intermediate image, and

wherein when a focal length at a Fresnel height hc corresponding to a display image plane center of the screen is FL(hc), within a plane including a central principal ray immediately before reaching the screen and a normal line of the screen at a point which the ray reaches, a focal length, at a Fresnel height hb, of a principal ray of a beam incident on the screen at a smallest angle of incidence is FL(hb), a focal length, at a Fresnel height ht, of a principal ray of a beam incident on the screen at a largest angle of incidence is FL(ht), a largest focal length and a smallest focal length over the entire screen are FLmax and FLmin, respectively, then conditional formulae (3) and (4) below are satisfied:

|(FLmax−

FLmin)/FL(hc)|>

0.1 

 

(3),

FL(ht)>

FL(hb) 

 

(4).

5. The rear projector according to claim 1,

wherein the projection optical system is a nonaxisymmetric projection optical system that forms an intermediate image, and

wherein when a focal length at a Fresnel height hc corresponding to a display image plane center of the screen is FL(hc), within a plane including a central principal ray immediately before reaching the screen and a normal line of the screen at a point which the ray reaches, a focal length, at a Fresnel height hb, of a principal ray of a beam incident on the screen at a smallest angle of incidence is FL(hb), a focal length, at a Fresnel height ht, of a principal ray of a beam incident on the screen at a largest angle of incidence is FL(ht), a largest focal length and a smallest focal length over the entire screen are FLmax and FLmin, respectively, then conditional formulae (3) and (5) below are satisfied:

|(FLmax−

FLmin)/FL(hc)|>

0.1 

 

(3),

FL(ht)<

FL(hb) 

 

(5).

6. The rear projector according to claim 1,

wherein when θ

min is a minimum angle of incidence on the screen, then conditional formula (6) below is satisfied;

40°

<

θ

min 

 

(6).

7. The rear projector according to claim 1,

wherein when θ

max is a maximum angle of incidence on the screen, then conditional formula (7) below is satisfied;

70<

θ

max<

85°

 

 

(7).

8. The rear projector according to claim 1,

wherein the Fresnel lens has spherical aberration in accordance with a height from a central axis of the Fresnel lens.

9. The rear projector according to claim 2,

wherein the projection optical system has a refractive lens and curved reflection surfaces, the curved reflection surface on a most screen side being a convex surface formed of a free curved surface.

10. The rear projector according to claim 2,

wherein conditional formula (1a) below is satisfied:

0.6<

FO/OQ<

0.9 

 

(1a).

11. The rear projector according to claim 3,

wherein the projection optical system has:

a refractive lens group formed of a plurality of refractive lenses; and

a concave reflection surface formed of a free curved surface arranged on an optical path on a screen side of the refractive lens group.

12. The rear projector according to claim 3,

wherein conditional formula (2a) below is satisfied:

1.1<

FO/OQ<

1.4 

 

(2a).

13. The rear projector according to claim 9,

wherein the projection optical system has four curved reflection surfaces.

14. The rear projector according to claim 9,

wherein the projection optical system has:

a refractive lens group formed of a plurality of refractive lenses; and

two curved reflection surfaces arranged on an optical path on a screen side of the refractive lens group.