Image display apparatus

Abstract

An image display apparatus which enables observation of a clear image at a wide field angle with substantially no reduction in the brightness of the image, and which is extremely small in size and light in weight and hence unlikely to cause the observer to be fatigued. The apparatus includes an image display device (6) and an ocular optical system (9) for leading an image of the display device (6) to an observer's eyeball (1). The ocular optical system (9) has a first optical element (7) and a second optical element (8). The first optical element (7) has three surfaces, and a space formed by the surfaces is filled with a medium having a refractive index larger than 1. The three surfaces are, in the order of backward ray tracing from the observer's eyeball (1) toward the image display device (6), a first surface (3) serving as both a refracting surface and an internally reflecting surface, a second surface (4) which is a reflecting surface of positive power facing the first surface (3) and decentered or tilted with respect to an observer's visual axis (2), and a third surface (5) which is a refracting surface closest to the image display device (6). The second optical element (8) has refracting action and is disposed between the first surface (3) and the observer's eyeball (1).

What I claim is:  
     
       1. An image display apparatus comprising an image display device for displaying an image, and an ocular optical system for projecting the image displayed by said image display device and for leading the projected image to an observer's eyeball, 
       said ocular optical system including a first optical element and a second optical element,  
       said first optical element having at least three surfaces, wherein a space formed by said at least three surfaces is filled with a medium having a refractive index larger than 1, said at least three surfaces being, in order in which light rays pass according to backward ray tracing from said observer's eyeball toward said image display device, a first surface which serves as both a refracting surface and an internally reflecting surface, a second surface which is a reflecting surface of positive power facing said first surface and decentered or tilted with respect to an observer's visual axis, and a third surface which is a refracting surface closest to said image display device,  
       said second optical element having refracting action and being disposed between said first surface and said observer's eyeball.  
     
     
       2. An image display apparatus according to claim  1 , wherein said second optical element has positive power. 
     
     
       3. An image display apparatus according to claim  2 , wherein said second optical element is a positive lens. 
     
     
       4. An image display apparatus according to claim  1  or  2 , wherein said second optical element is a cemented lens. 
     
     
       5. An image display apparatus according to claim  1  or  2 , wherein said second optical element is a special  prism comprising two decentered optical surfaces. 
     
     
       6. An image display apparatus according to claim  1 , wherein said second optical element is decentered or tilted with respect to said observer's visual axis. 
     
     
       7. An image display apparatus according to claim  1 , wherein internal reflection at the first surface of said first optical element is total reflection. 
     
     
       8. An image display apparatus according to claim  1 , wherein the first surface of said first optical element has an internally reflecting region which has been mirror-coated. 
     
     
       9. An image display apparatus according to claim  1 , wherein at least one of the first, second and third surfaces of said first optical element is a decentered aspherical surface. 
     
     
       10. An image display apparatus according to claim  9 , wherein at least one of the first, second and third surfaces of said first optical element is an anamorphic surface. 
     
     
       11. An image display apparatus according to claim  10 , which satisfies the following condition: 
       
         
           R y2 /R x2 ≧1   (1)  
         
       
       where, assuming that a vertical plane containing said observer's visual axis is defined as a YZ-plane, and a horizontal plane containing said observer's visual axis is defined as an XZ-plane, R y2  is a radius of curvature in the YZ-plane of the second surface of said first optical element, and R x2  is a radius of curvature in the XZ-plane of said second surface. 
     
     
       12. An image display apparatus according to claim  1 , wherein the first surface of said first optical element is a reflecting surface having a convex surface directed toward said second surface. 
     
     
       13. An image display apparatus according to claim  1 , wherein at least one of the first and third surfaces of said first optical element is tilted or decentered with respect to said observer's visual axis. 
     
     
       14. An image display apparatus according to claim  1 , which satisfies the following condition: 
       
         
           5°<α<30°  (2)  
         
       
       where α is an angle formed between a line normal to the second surface of said first optical element and an axial principal ray. 
     
     
       15. An image display apparatus according to claim  1 ,  9  or  10 , wherein said image display device has a display surface tilted with respect to said observer's visual axis. 
     
     
       16. An image display apparatus according to claim  1 ,  9  or  10 , further comprising means for positioning both said image display device and said ocular optical system with respect to an observer's head. 
     
     
       17. An image display apparatus according to any one of claims  1  to  16 ,  claim  1 ,  9  or  10 , further comprising means for supporting both said image display device and said ocular optical system with respect to an observer's head so that said image display apparatus can be fitted to said observer's head. 
     
     
       18. An image display apparatus according to claim  1 ,  9  or  10 , further comprising means for supporting at least a pair of said image display apparatuses at a predetermined spacing. 
     
     
       19. An image display apparatus according to claim  1 ,  9  or  10 , wherein said ocular optical system is used as an imaging optical system. 
     
     
       20. An imaging optical system for forming an object image as an image plane, 
       
         said imaging optical system comprising:  
       
       
         an optical unit disposed between a pupil and said image plane,  
       
       
         said optical unit including a first optical element and a second optical element,  
       
       
         said first optical element having at least three surfaces,  
       
       
         wherein a space formed by said at least three surfaces is filled with a medium having a refractive index larger than  1 ,  
       
       
         said at least three surfaces being, in order in which light rays pass according to ray tracing from said pupil toward said image plane, a first surface which serves as both a refracting surface and an internally reflecting surface, a second surface which is a reflecting surface of positive power facing said first surface and which is one of decentered and tilted with respect to an optical axis, and a third surface which is a refracting surface closest to said image plane,  
       
       
         said second optical element having refracting action and being disposed between said first surface and said pupil. 
       
     
     
       21. An imaging optical system according to claim  20 , wherein said second optical element has positive power. 
     
     
       22. An imaging optical system according to claim  21 , wherein said second optical element is a positive lens. 
     
     
       23. An imaging optical system according to claim  20  or  21 , wherein said second optical element is a cemented lens. 
     
     
       24. An imaging optical system according to claim  20  or  21 , wherein said second optical element is a special prism comprising two decentered optical surfaces. 
     
     
       25. An imaging optical system according to claim  20 , wherein said second optical element is one of decentered and tilted with respect to said optical axis. 
     
     
       26. An imaging optical system according to claim  20 , wherein internal reflection at the first surface of said first optical element is total reflection. 
     
     
       27. An imaging optical system according to claim  20 , wherein the first surface of said first optical element has an internally reflecting region which has been mirror- coated.   
     
     
       28. An imaging optical system according to claim  20 , wherein at least one of the first, second and third surfaces of said first optical element is a decentered aspherical surface. 
     
     
       29. An imaging optical system according to claim  28 , wherein at least one of the first, second and third surfaces of said first optical element is an anamorphic surface. 
     
     
       30. An imaging optical system according to claim  29 , which satisfies the following condition: 
       
         
           
             R 
             y2 
             /R 
             x2 
             ≧ 1   
           
         
       
         where, assuming that a vertical plane containing said optical axis is defined as a YZ - plane, and a horizontal plane containing said optical axis is defined as an XZ - plane, R   y2    is a radius of curvature in the YZ plane of the second surface of said first optical element, and R   x2    is a radius of curvature in the XZ - plane of said second surface.   
     
     
       31. An imaging optical system according to claim  20 , wherein the first surface of said first optical element is a reflecting surface having a convex surface directed toward said second surface. 
     
     
       32. An imaging optical system according to claim  20 , wherein at least one of the first and third surfaces of said first optical element is one of tilted and decentered with respect to said optical axis. 
     
     
       33. An imaging optical system according to claim  20 , which satisfies the following condition: 
       
         
           
               5 °<α< 30  ° 
           
         
       
       
         where α is an angle formed between a line normal to the second surface of said first optical element and an axial principal ray. 
       
     
     
       34. An imaging optical system according to claim  20 ,  28  or  29 , wherein the image plane where said object image is formed is tilted with respect to said optical axis. 
     
     
       35. An imaging optical system according to claim  20 ,  28  or  29 , including: 
       
         a front unit placed on an object side of said pupil, and  
       
       
         a rear unit having said optical unit. 
       
     
     
       36. An imaging optical system according to claim  35 , wherein said front unit comprises an optical system having positive power as a whole. 
     
     
       37. A camera apparatus comprising: 
       
         the imaging optical system of claim  20 ,  28  or  29 , said imaging optical system being incorporated as means for forming an object image. 
       
     
     
       38. A finder optical system comprising: 
       
         the imaging optical system of claim  20 ,  28  or  29 ;  
       
         an image - erecting optical system for erecting said object image; and    
       
         an ocular optical system for viewing said object image. 
       
     
     
       39. A camera apparatus comprising: 
       
         the finder optical system of claim  38 ; and  
       
       
         a photographic optical system provided in parallel to said finder optical system. 
       
     
     
       40. A camera apparatus comprising: 
       
         the imaging optical system of claim  35 , said imaging optical system being incorporated as means for forming an object image. 
       
     
     
       41. A finder optical system comprising: 
       
         the imaging optical system of claim  35 ;  
       
         an image - erecting optical system for erecting said object image; and    
       
         an ocular optical system for viewing said object image. 
       
     
     
       42. A camera apparatus comprising: 
       
         the finder optical system of claim  41 ; and  
       
       
         a photographic optical system provided in parallel to said finder optical system. 
       
     
     
       43. A viewing optical system comprising: 
         image - forming means for forming an observation image as an image plane, and    
         an ocular optical system for projecting the observation image formed by said image - forming means and for leading the projected image to an observer's eyeball,    
       
         said ocular optical system including a first optical element and a second optical element,  
       
       
         said first optical element having at least three surfaces,  
       
       
         wherein a space formed by said at least three surfaces is filled with a medium having a refractive index larger than  1 ,  
       
       
         said at least three surfaces being, in order in which light rays pass according to backward ray tracing from said observer's eyeball toward said image forming means, a first surface which serves as both a refracting surface and an internally reflecting surface, a second surface which is a reflecting surface of positive power facing said first surface and which is one of decentered and tilted with respect to an observer's visual axis, and a third surface which is a refracting surface closest to the image plane of said observation image,  
       
       
         said second optical element having refracting action and being disposed between said first surface and said observer's eyeball. 
       
     
     
       44. A viewing optical system according to claim  43 , wherein said second optical element has positive power. 
     
     
       45. A viewing optical system according to claim  44 , wherein said second optical element is a positive lens. 
     
     
       46. A viewing optical system according to claim  43  or  44 , wherein said second optical element is a cemented lens. 
     
     
       47. A viewing optical system according to claim  43  or  44 , wherein said second optical element is a prism comprising two decentered optical surfaces. 
     
     
       48. A viewing optical system according to claim  43 , wherein said second optical element is one of decentered and tilted with respect to said observer's visual axis. 
     
     
       49. A viewing optical system according to claim  43 , wherein internal reflection at the first surface of said first optical element is total reflection. 
     
     
       50. A viewing optical system according to claim  43 , wherein the first surface of said first optical element has an internally reflecting region which has been mirror- coated.   
     
     
       51. A viewing optical system according to claim  43 , wherein at least one of the first, second and third surfaces of said first optical element is a decentered aspherical surface. 
     
     
       52. A viewing optical system according to claim  51 , wherein at least one of the first, second and third surfaces of said first optical element is an anamorphic surface. 
     
     
       53. An viewing optical system according to claim  52 , which satisfies the following condition: 
       
         
           
             R 
             y2 
             /R 
             x2 
             ≧ 1   
           
         
       
         where, assuming that a vertical plane containing said observer's visual axis is defined as a YZ - plane, and a horizontal plane containing said observer's visual axis is defined as an XZ - plane, R   y2    is a radius of curvature in the YZ - plane of the second surface of said first optical element, and R   x2    is a radius of curvature in the XZ - plane of said second surface.   
     
     
       54. A viewing optical system according to claim  43 , wherein the first surface of said first optical element is a reflecting surface having a convex surface directed toward said second surface. 
     
     
       55. A viewing optical system according to claim  43 , wherein at least one of the first and third surfaces of said first optical element is tilted or decentered with respect to said observer's visual axis. 
     
     
       56. A viewing optical system according to claim  43 , which satisfies the following condition: 
       
         
           
               5 °<α< 30 ° 
           
         
       
       
         where α is an angle formed between a line normal to the second surface of said first optical element and an axial principal ray. 
       
     
     
       57. A viewing optical system according to claim  43 ,  51  or  52 , wherein the image plane of said observation image is tilted with respect to said observer's visual axis.