Oblique projection optical system

• US 20060164605A1
• Filed: 11/03/2005
• Published: 07/27/2006
• Est. Priority Date: 11/10/2004
• Status: Active Grant

• Current Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Inventors: Kuwa, Tomiei
• Granted Patent: US 7,670,008 B2
• Time in Patent Office: Days
• US Class Current: 353/78
• CPC Class Codes: G02B 17/0848 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: 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

Abstract

In an oblique projection optical system for performing enlargement projection from a primary image surface on the reduction side to a secondary image surface on the enlargement side, at least one reflective surface having an optical power is provided, and, assuming that of the aforementioned surfaces, the reflective surface located on the most secondary image surface side in the optical path is a first curved reflective surface, the first curved reflective surface has a portion having a positive optical power and a portion having a negative optical power.

Claims

1. An oblique projection optical system for performing enlargement projection from a primary image surface on a reduction side to a secondary image surface on an enlargement side,

wherein at least one reflective surface having an optical power is provided, and

wherein, assuming that of said at least one reflective surface, the reflective surface located on a most secondary image surface side in an optical path is a first curved reflective surface, the first curved reflective surface has a portion having a positive optical power and a portion having a negative optical power.

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

wherein, assuming that a principal ray emitted from a center of the primary image surface and passing through a center of an aperture stop is a central principal ray, the first curved reflective surface includes at an intersection thereof with the central principal ray a direction having a positive optical power and a direction having a negative optical power.

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

wherein the direction having a positive optical power and the direction having a negative optical power are two directions orthogonal to each other at the intersection.

4. The oblique projection optical system according to claim 3

wherein the two directions orthogonal to each other at the intersection correspond to an image vertical direction and an image horizontal direction.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, and that an XiYi plane including a center of the secondary image surface is a PXiYi plane, an effective optical region of the first curved reflective surface on an optical extension plane of the PXiYi plane is formed of a concavely shaped portion having a positive optical power and a convexly shaped portion having a negative optical power.

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

wherein at least one rotation-symmetric optical element is provided which has an optical power and whose rotation-symmetric shape is formed at least partly with either of a reflective surface or a refractive surface, and

wherein, assuming that a direction normal to the primary image surface is an Xo direction, that an image shorter-side direction of the primary image surface is a Yo direction, and that an XoYo plane including a center of the primary image surface is a PXoYo plane, a rotation center axis of said at least one rotation-symmetric optical element lies within an optical extension plane of the PXoYo plane and also is not parallel to an optical extension direction of the Xo direction.

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

wherein at least one refractive optical element having an aberration correction capability is provided.

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

wherein the refractive optical element has at least one refractive surface formed with an aspherical surface.

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

wherein at least one rotation-asymmetric optical surface is provided.

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

wherein the rotation-asymmetric optical surface is a refractive surface so formed as to be rotation-asymmetric.

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

wherein the rotation-asymmetric optical surface is a reflective surface so formed as to be rotation-asymmetric.

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

wherein at least two reflective surfaces each having an optical power are provided.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, that an XiYi plane including a center of the secondary image surface is a PXiYi plane, that, of beams on the PXiYi plane that reach the secondary image surface, the beam having a principal ray which forms a largest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

max and the beam having a principal ray which forms a smallest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

min, that a direction perpendicular to an optical extension plane of the PXiYi plane is a Zi direction, and that, of the reflective surfaces each having an optical power, the reflective surface located at a second position when counted from a secondary image surface side is a second curved reflective surface, the second curved reflective surface fulfill conditional formula (2) below;

(CoR2Zmax−

CoR2Zmin)>

0  

 

(2)

where

CoR2Zmax represents a curvature of the second curved reflective surface in the Zi direction near a region where the beam RaysXiYiθ

max is reflected on the second curved reflective surface on the optical extension plane of the PXiYi plane, and

CoR2Zmin represents a curvature of the second curved reflective surface in the Zi direction near a region where the beam RaysXiYiθ

min is reflected on the second curved reflective surface on the optical extension plane of the PXiYi plane.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, that an XiYi plane including a center of the secondary image surface is a PXiYi plane, that, of beams on the PXiYi plane that reach the secondary image surface, the beam having a principal ray which forms a largest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

max and the beam having a principal ray which forms a smallest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

min, and that, of the reflective surfaces each having an optical power, the reflective surface located at a second position when counted from a secondary image surface side is a second curved reflective surface, along a line, where the second curved reflective surface and an optical extension plane of the PXiYi plane intersect each other, from a region where the beam RaysXiYiθ

max is reflected to a region where the beam RaysXiYiθ

min is reflected, there exists a range such that a curvature on this line once becomes large and then small.

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

wherein a maximum value of an angle of incidence that is formed by a principal ray of a projected beam with respect to the secondary image surface is 65 degrees or more, and

wherein conditional formula (3) below is fulfilled:

1.05<

(α

max/α

min)<

3  

 

(3)

where

α

max represents the maximum value (in degrees) of the angle of incidence that is formed by the principal ray of the projected beam with respect to the secondary image surface, and

α

min represents a minimum value (in degrees) of the angle of incidence that is formed by the principal ray of the projected beam with respect to the secondary image surface.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, that an XiYi plane including a center of the secondary image surface is a PXiYi plane, that, of beams on the PXiYi plane that reach the secondary image surface, the beam having a principal ray which forms a largest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

max and the beam having a principal ray which forms a smallest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

min, and that a direction perpendicular to an optical extension plane of the PXiYi plane is a Zi direction, conditional formula (4) below is fulfilled;

(CoR1Zmin−

CoR1Zmax)>

0  

 

(4)

where

CoR1Zmax represents a curvature of the first curved reflective surface in the Zi direction near a region where the beam RaysXiYiθ

max is reflected on the first curved reflective surface on the optical extension plane of the PXiYi plane, and

CoR1Zmin represents a curvature of the first curved reflective surface in the Zi direction near a region where the beam RaysXiYiθ

min is reflected on the first curved reflective surface on the optical extension plane of the PXiYi plane.

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

wherein conditional formula (5) below be fulfilled:

(CoR1Zmin−

CoR1Ymin)/(CoR1Zmax−

CoR1Ymax)>

1  

 

(5)

where

CoR1Ymax represents a curvature of the first curved reflective surface in the Yi direction near the region where the beam RaysXiYiθ

max is reflected on the first curved reflective surface on the optical extension plane of the PXiYi plane, and

CoR1Ymin represents a curvature of the first curved reflective surface in the Yi direction near the region where the beam RaysXiYiθ

min is reflected on the first curved reflective surface on the optical extension plane of the PXiYi plane.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, that an XiYi plane including a center of the secondary image surface is a PXiYi plane, and that, of beams on the PXiYi plane that reach the secondary image surface, the beam having a principal ray which forms a largest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

max and the beam having a principal ray which forms a smallest angle with the Xi direction when incident on the secondary image surface is RaysXiYiθ

min, a shape of an effective optical region of the first curved reflective surface on an optical extension plane of the PXiYi plane is a concave having a positive optical power at a region where the beam RaysXiYiθ

max is reflected and is a convex having a negative optical power at a region where the beam RaysXiYiθ

min is reflected.

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

wherein, assuming that a principal ray emitted from a center of the primary image surface and then passing through a center of an aperture stop is a central principal ray, and that a curvature on a line where the optical extension plane of the PXiYi plane and the first curved reflective surface intersect each other is CoR1Y, a point at which a sign of the curvature CoR1Y is reversed is located closer to the region where the beam RaysXiYiθ

min is reflected than the intersection of the central principal ray and the first curved reflective surface.

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

wherein, assuming that a direction normal to the secondary image surface is an Xi direction, that an image shorter-side direction of the secondary image surface is a Yi direction, that an XiYi plane including a center of the secondary image surface is a PXiYi plane, that a direction normal to the primary image surface is an Xo direction, that an image shorter side direction of the primary surface is a Yo direction, and that an XoYo plane including a center of the primary image surface is a PXoYo plane, an optical extension plane of the PXoYo plane and an optical extension plane of the PXiYi plane are on the same plane.

21. An image projection apparatus comprising:

an image display device that forms an image to be projected;

a light source;

an illumination optical system that guides light from the light source to the image display device; and

a projection optical system that obliquely projects on a screen an image formed by the image display device,

wherein the projection optical system has at least one reflective surface having an optical power, and

wherein, of said at least one reflective surface having an optical power, a first curved reflective surface located on a most screen side has a portion having a positive optical power and a portion having a negative optical power.

22. An oblique projection optical system for performing enlargement projection from a primary image surface on a reduction side to a secondary image surface on an enlargement side, the oblique projection optical system comprising:

in order along a projection optical path from a secondary image surface side,

a first curved reflective surface;

a second curved reflective surface;

a third curved reflective surface having a negative optical power; and

a fourth curved reflective surface having a positive optical power,

wherein the first curved reflective surface has a portion having a positive optical power and a portion having a negative optical power.

23. The oblique projection optical system according to claim 22, further comprising,

a rotation-asymmetric aspherical surface lens that is arranged between the third curved reflective surface and the fourth curved reflective surface.

24. An oblique projection optical system for performing enlargement projection from a primary image surface on a reduction side to a secondary image surface on an enlargement side, the oblique projection optical system comprising:

in order along a projection optical path from a secondary image surface side,

a first curved reflective surface; and

a lens unit having a plurality of lens elements,

wherein the first curved reflective surface has a portion having a positive optical power and a portion having a negative optical power.

25. The oblique projection optical system according to claim 24, further comprising

a reflective surface that is arranged between the lens unit and the first curved reflective surface.

26. The oblique projection optical system according to claim 25,

wherein the reflective surface arranged between the lens unit and the first curved reflective surface is a curved reflective surface.

27. The oblique projection optical system according to claim 25,

wherein the reflective surface arranged between the lens unit and the first curved reflective surface is a flat curved reflective surface, which bends the projection optical path such that a direction normal to the secondary image surface and an image longer-side direction of the primary image surface are parallel to each other.