OBLIQUE PROJECTION OPTICAL SYSTEM

• US 20090168031A1
• Filed: 12/22/2008
• Published: 07/02/2009
• Est. Priority Date: 12/27/2007
• Status: Active Grant

• Current Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Inventors: Imaoka, Masayuki, Yamada, Keiko
• Granted Patent: US 8,052,283 B2
• Time in Patent Office: Days
• US Class Current: 353/99
• 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 17/0816 off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
• CPC Class Codes: G02B 17/0852 having a field corrector only
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066

Abstract

An oblique projection optical system enlarges an image formed on a display device surface, and obliquely projects the enlarged image on a screen surface. The oblique projection optical system has, in the order from a reduction side: a refraction optical portion having a positive optical power, a concave reflection surface having a positive optical power, and a convex reflection surface having a negative optical power. The refraction optical portion includes a rotationally symmetric coaxial refraction group. An intermediate image of the image formed on the display device surface is formed between the refraction optical portion and the concave reflection surface. An aperture stop image is formed between the concave reflection surface and the convex reflection surface. The concave reflection surface and the convex reflection surface fulfill prescribed conditional formulae.

Claims

1. An oblique projection optical system that enlarges an image formed on a display device surface, and obliquely projects the enlarged image on a screen surface, the oblique projection optical system comprising, in the order from a reduction side:

a refraction optical portion having a positive optical power;

a concave reflection surface having a positive optical power; and

a convex reflection surface having a negative optical power,

wherein

the refraction optical portion includes a rotationally symmetric coaxial refraction group,

an intermediate image of the image formed on the display device surface is formed between the refraction optical portion and the concave reflection surface,

an aperture stop image is formed between the concave reflection surface and the convex reflection surface,

and conditional formulae (1) and (2) below are fulfilled;

0.3<

L2/L1<

1  

 

(1),

0.2<

|f1/f2|<

 

 

(2),

where, when a principal ray that is emitted from the image center on the display device surface and reaches the image center on the screen surface is called a central principal ray,

L1 represents a distance that is in the normal direction of the display device surface and extends from the image center on the display device surface from which the central principal ray is emitted to a point where the central principal ray hits the concave reflection surface;

L2 represents a distance that is in the normal direction of the screen surface and extends from a point where the central principal ray hits the concave reflection surface to a point where the central principal ray hits the convex reflection surface;

f1 represents a focal length of the concave reflection surface at the point where the central principal ray hits the concave reflection surface; and

f2 represents a focal length of the convex reflection surface at the point where the central principal ray hits the convex reflection surface.

2. The oblique projection optical system according to claim 1,

wherein conditional formula (3) below is fulfilled:

0.2<

f0/f1<

1  

 

(3),

where

f0 represents a paraxial focal length of the rotationally symmetric coaxial refraction group.

3. The oblique projection optical system according to claim 1,

wherein conditional formula (4) below is fulfilled:

0.5<

p/L1<

0.9  

 

(4),

where, in a plane that contains the central principal ray immediately before it hits the screen surface, and the normal of the screen surface at the image center on the screen surface, p1 is a point where a tracing-back ray of a first principal ray, which is a principal ray of a light beam hitting the screen surface at the largest incident angle and hits the concave reflection surface, meets with a tracing-back ray of a second principal ray which is a principal ray of a light beam hitting the screen surface at the smallest incident angle and hits the concave reflection surface, and p2 is the mid-point between a point where the first principal ray, hits the concave reflection surface, and a point where the second principal ray, hits the concave reflection surface, wherein p is the distance which extends from the point p1 to the point p2 and is in the normal direction of the display device surface.

4. The oblique projection optical system according to claim 1,

wherein a lens element disposed at a most enlargement-side end of the refraction optical portion fulfills conditional formula (5) below:

0.2<

L3/L2<

1.5  

 

(5),

where

L3 represents a distance which is in the normal direction of the display device surface and extends from a point where the central principal ray hits the concave reflection surface to a point where the central principal ray hits a refraction surface on the enlargement side of the lens element disposed at the most enlargement-side end of the refraction optical portion.

5. The oblique projection optical system according to claim 1,

wherein focusing is carried out by moving only the concave reflection surface depending on change in the projection distance.

6. The oblique projection optical system according to claim 2,

wherein conditional formula (4) below is fulfilled:

0.5<

p/L1<

0.9  

 

(4),

where, in a plane that contains the central principal ray immediately before it hits the screen surface, and the normal of the screen surface at the image center on the screen surface, p1 is a point where a tracing-back ray of a first principal ray, which is a principal ray of a light beam hitting the screen surface at the largest incident angle and hits the concave reflection surface, meets with a tracing-back ray of a second principal ray which is a principal ray of a light beam hitting the screen surface at the smallest incident angle and hits the concave reflection surface, and p2 is the mid-point between a point where the first principal ray, hits the concave reflection surface, and a point where the second principal ray, hits the concave reflection surface, wherein p is the distance which extends from the point p1 to the point p2 and is in the normal direction of the display device surface.

7. The oblique projection optical system according to claim 2,

wherein focusing is carried out by moving only the concave reflection surface depending on change in the projection distance.

8. The oblique projection optical system according to claim 3,

wherein a lens element disposed at a most enlargement-side end of the refraction optical portion fulfills conditional formula (5) below:

0.2<

L3/L2<

1.5  

 

(5),

where

L3 represents a distance which is in the normal direction of the display device surface and extends from a point where the central principal ray hits the concave reflection surface to a point where the central principal ray hits a refraction surface on the enlargement side of the lens element disposed at the most enlargement-side end of the refraction optical portion.

9. The oblique projection optical system according to claim 3,

wherein focusing is carried out by moving only the concave reflection surface depending on change in the projection distance.

10. The oblique projection optical system according to claim 4,

wherein the oblique projection optical system has a rotationally asymmetric aspherical surface on the enlargement side of the coaxial refraction group, the aspherical surface does not share the optical axis with the coaxial refraction group, and is tilted in the same direction as that of the surface of the intermediate image.

11. The oblique projection optical system according to claim 6,

wherein a lens element disposed at a most enlargement-side end of the refraction optical portion fulfills conditional formula (5) below:

0.2<

L3/L2<

1.5  

 

(5),

where

L3 represents a distance which is in the normal direction of the display device surface and extends from a point where the central principal ray hits the concave reflection surface to a point where the central principal ray hits a refraction surface on the enlargement side of the lens element disposed at the most enlargement-side end of the refraction optical portion.

12. The oblique projection optical system according to claim 11,

wherein the oblique projection optical system has a rotationally asymmetric aspherical surface on the enlargement side of the coaxial refraction group, the aspherical surface does not share the optical axis with the coaxial refraction group, and is tilted in the same direction as that of the surface of the intermediate image.

13. The oblique projection optical system according to claim 8,

wherein the oblique projection optical system has a rotationally asymmetric aspherical surface on the enlargement side of the coaxial refraction group, the aspherical surface does not share the optical axis with the coaxial refraction group, and is tilted in the same direction as that of the surface of the intermediate image.

14. The oblique projection optical system according to claim 7,

wherein conditional formula (6) below is fulfilled:

0.5<

f1a/f1b<

2.2  

 

(6),

where, in a plane that contains the central principal ray immediately before it hits the screen surface, and the normal of the screen surface at the image center on the screen surface,

f1a represents the focal length of the concave reflection surface at a point where a principal ray of a light beam hitting the screen surface at the largest incident angle hits the concave reflection surface; and

f1b represents the focal length of the concave reflection surface at a point where a principal ray of a light beam hitting the screen surface at the smallest incident angle hits the concave reflection surface.

15. The oblique projection optical system according to claim 9,

wherein conditional formula (6) below is fulfilled:

0.5<

f1a/f1b<

2.2  

 

(6),

where, in a plane that contains the central principal ray immediately before it hits the screen surface, and the normal of the screen surface at the image center on the screen surface,

f1a represents the focal length of the concave reflection surface at a point where the first principal ray of a light beam hitting the screen surface at the largest incident angle hits the concave reflection surface; and

f1b represents the focal length of the concave reflection surface at a point where the second principal ray of a light beam hitting the screen surface at the smallest incident angle hits the concave reflection surface.

16. The oblique projection optical system according to claim 5,

wherein conditional formula (6) below is fulfilled:

0.5<

f1a/f1b<

2.2  

 

(6),

where, in a plane that contains the central principal ray immediately before it hits the screen surface, and the normal of the screen surface at the image center on the screen surface,

f1a represents the focal length of the concave reflection surface at a point where a principal ray of a light beam hitting the screen surface at the largest incident angle hits the concave reflection surface; and

f1b represents the focal length of the concave reflection surface at a point where a principal ray of a light beam hitting the screen surface at the smallest incident angle hits the concave reflection surface.

17. The oblique projection optical system according to claim 7,

wherein the direction in which the concave refraction surface is moved is tilted to the normal direction of the display device surface and fulfills conditional formula (7) below:

10°

<

θ

<

70°

 

 

(7),

where

θ

represents an angle (acute angle) between the axis along which the concave reflection surface is moved and the normal of the display device surface.

18. The oblique projection optical system according to claim 9,

wherein the direction in which the concave refraction surface is moved is tilted to the normal direction of the display device surface and fulfills conditional formula (7) below:

10°

<

θ

<

70°

 

 

(7),

where

θ

represents an angle (acute angle) between the axis along which the concave reflection surface is moved and the normal of the display device surface.

19. The oblique projection optical system according to claim 5,

wherein the direction in which the concave refraction surface is moved is tilted to the normal direction of the display device surface and fulfills conditional formula (7) below:

10°

<

θ

<

70°

 

 

(7),

where

θ

represents an angle (acute angle) between the axis along which the concave reflection surface is moved and the normal of the display device surface.

20. An image projection apparatus comprising:

a display device which forms a 2-dimensional image; and

an oblique projection optical system which enlarges the 2-dimensional image formed by the display device and projects the enlarged image on a screen surface, the oblique projection optical system includes, in the order from a reduction side;

a refraction optical portion having a positive optical power;

a concave reflection surface having a positive optical power; and

a convex reflection surface having a negative optical power,

wherein

the refraction optical portion includes a rotationally symmetric coaxial refraction group,

an intermediate image of the 2-dimensional image is formed between the refraction optical portion and the concave reflection surface,

an aperture stop image is formed between the concave reflection surface and the convex reflection surface,

and conditional formulae (1) and (2) below are fulfilled;

0.3<

L2/L1<

1  

 

(1),

0.2<

|f1/f2|<

1  

 

(2),

where, when a principal ray that is emitted from the image center on the display device surface and reaches the image center on the screen surface is called a central principal ray,

L1 represents a distance that is in the normal direction of the display device surface and extends from the image center on the display device surface from which the central principal ray is emitted to a point where the central principal ray hits the concave reflection surface;

L2 represents a distance that is in the normal direction of the screen surface and extends from a point where the central principal ray hits the concave reflection surface to a point where the central principal ray hits the convex reflection surface;

f1 represents a focal length of the concave reflection surface at the point where the central principal ray hits the concave reflection surface; and

f2 represents a focal length of the convex reflection surface at the point where the central principal ray hits the convex reflection surface.