Projection optical system and visual display apparatus using the same

• US 20100157255A1
• Filed: 12/10/2009
• Published: 06/24/2010
• Est. Priority Date: 12/16/2008
• Status: Abandoned Application

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Togino, Takayoshi
• Application Number:
  US12/653,233
• Publication Number:
  US 20100157255A1
• Time in Patent Office: Days
• US Class Current: 353/69
• CPC Class Codes: G03B 21/147 Optical correction of image distortions, e.g. keystone

Abstract

In a projection optical system 4 for projecting an image being displayed on an image display element 3, the display surface of the image display element 3 and the projection surface of the projection optical system 4 are decentered in the Y-Z cross section and the projection surface is formed by means of a circular-arc-shaped curved surface with the chord thereof directed to the side of the projection optical system 4 in the X-Z cross section and the projection optical system 4 has at least a rotationally asymmetric corrective optical surface 5 for correcting the distortion of the image.

Claims

1. A projection optical system for projecting an image being displayed on an image display element, comprising:

a projection surface of the projection optical system is formed by means of a circular-arc-shaped curved surface having a center line at the side of the projection optical system in an X-Z cross section; and

at least a rotationally asymmetric corrective optical surface that corrects the distortion of the image on the projection surface is provided,

wherein a display surface of the image display element and a projection surface of the projection optical system are decentered in a Y-Z cross section.

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

the display surface and the projection surface are in parallel with each other and shifted and decentered in the Y-Z cross section, and

the corrective optical surface corrects a bow-like image distortion that arises due to the cylindrical projection surface to which a flux of light is projected obliquely in the Y-Z cross section.

3. The projection optical system according to claims 2, wherein

an angle of the corrective optical surface changes symmetrically relative to the Y-Z cross section as the corrective optical surface is moved away from the Y-Z cross section in a positive direction and in a negative direction along an X-axis.

4. The projection optical system according to claim 2, wherein

the corrective optical surface directs rays of light toward the opposite side relative to a central axis of the projection optical system as the corrective optical surface moves away from the Y-Z cross section in the positive direction and the negative direction along the X-axis to correct the bow-like image distortion that arises with a chord thereof facing the central axis side of the projection optical system and a circular arc thereof facing the opposite relative to the central axis of the projection optical system in the X-Y plane.

5. The projection optical system according to claim 3, wherein

the corrective optical surface directs rays of light toward the opposite side relative to the central axis of the projection optical system as the corrective optical surface moves away from the Y-Z cross section in the positive direction and the negative direction along the X-axis to correct the bow-like image distortion that arises with the chord thereof facing the central axis side of the projection optical system and the circular arc thereof facing the opposite relative to the central axis of the projection optical system in the X-Y plane.

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

the corrective optical surface gives a C8 term (x²y term) when the corrective optical surface is formed by means of a free-form surface defined by formula (a) represented below:

$\begin{array}{cc}Z=\left(r^2/R\right)/\left[1+\surd <br><br>\left\{1-\left(1+k\right)<br><br>{\left(r/R\right)}^2\right\}\right]+\underset{j=1}{\overset{\mathrm{\infty <br><br>}}{\sum <br><br>}}<br><br><br><br>C_j<br><br>X^m<br><br>Y^n,& \left(a\right)\end{array}$

where R;

radius of curvature at the vertex,

k;

conic constant and

r=√

(X²+Y²).

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

the display surface and the projection surface are tilted and decentered to form an angle in the Y-Z cross section and the corrective optical surface has at least two rotationally asymmetric surfaces for correcting the image distortion on the projection surface.

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

the at least two corrective optical surfaces correct simultaneously the bow-like image distortion and a trapezoidal imaging distortion that arise when the angle between the surfaces changes as the surfaces moves away from the Y-Z cross section in the positive direction and the negative direction of the X-axis.

9. The projection optical system according to claim 7, wherein

the corrective optical surface has at least two surfaces for correcting rays of light in the opposite directions toward the positive direction and the negative direction of the Y-axis as the corrective optical surface moves away from the Y-Z surface in the positive direction and the negative direction of the X-axis to correct simultaneously the bow-like image distortion and the trapezoidal imaging distortion.

10. The projection optical system according to claim 8, wherein

the corrective optical surface has at least two surfaces for correcting rays of light in the opposite directions toward the positive direction and the negative direction of the Y-axis as the corrective optical surface moves away from the Y-Z surface in the positive direction and the negative direction of the X-axis to correct simultaneously the bow-like image distortion and the trapezoidal imaging distortion.

11. The projection optical system according to claim 7, wherein

the at least two corrective optical surfaces give a C8 term (x²y term) when the corrective optical surfaces are formed by means of respective free-form surfaces defined by formula (a) represented below:

$\begin{array}{cc}Z=\left(r^2/R\right)/\left[1+\surd <br><br>\left\{1-\left(1+k\right)<br><br>{\left(r/R\right)}^2\right\}\right]+\underset{j=1}{\overset{\mathrm{\infty <br><br>}}{\sum <br><br>}}<br><br><br><br>C_j<br><br>X^m<br><br>Y^n,& \left(a\right)\end{array}$

where R;

radius of curvature at the vertex,

k;

conic constant and

r=√

(X²+Y²).

12. A visual display apparatus comprising:

the projection optical system according to claim 1;

a diffusion surface arranged near the image projected by the projection optical system; and

an eyepiece optical system having positive reflection power for a remote virtual image that is the image projected by the projection optical system,

wherein, the image projected by the eyepiece optical system, the diffusion surface and the projection optical system being arranged so as to draw a circular arc at an arbitrary position in a plane orthogonal relative to the common axis of rotational symmetry.

13. The visual display apparatus according to claim 12, wherein

a conditional formula (1) represented below is satisfied:

400<

R 

 

(1),

where R is the radius of curvature of a part (near a visual axis) of the eyepiece optical system that a central main ray of light from the projection optical system strikes.

14. The visual display apparatus according to claim 12, wherein

the diffusion surface is toric-surface-shaped.

15. The visual display apparatus according to claim 12, wherein

the eyepiece optical system is a spherical surface.

16. The visual display apparatus according to claim 12, wherein

the eyepiece optical system is a toric surface.

17. The visual display apparatus according to claim 12, wherein

the corrective optical surface is formed by a light transmitting element.

18. The visual display apparatus according to claim 15, wherein

the light transmitting element has a free-form surface.