Optical system and optical 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 observation image, and which is extremely small in size and light in weight. The image display apparatus has an image display device (7) and an ocular optical system (8) for projecting the image of the image display device (7) and leading the projected image to an observer's eyeball (1). The ocular optical system (8) has at least three optical surfaces, and a space formed by these surfaces is filled with a medium having a refractive index larger than 1. The three optical surfaces are defined as a first surface (3), a second surface (4), and a third surface (5), respectively, in the order in which light rays pass in backward ray tracing from the observer's eyeball (1) to the image display device (7). The optical surfaces are disposed such that light rays from the observer's eyeball (1) pass through the first surface (3) and are reflected by the second surface (4) and further reflected by the third surface (5), which is a reflecting surface having positive power, and the light rays reflected by the third surface (5) are reflected by the first surface (3) and pass through the second surface (4) to reach the image display device (7).

What we 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 having at least three optical surfaces, wherein a space formed by said at least three optical surfaces is filled with a medium having a refractive index larger than 1,  
       said at least three optical surfaces being defined as a first surface, a second surface, and a third surface, respectively, in order in which light rays pass in backward ray tracing from said observer's eyeball to said image display device, and  
       said at least three optical surfaces being disposed such that light rays pass in said backward ray tracing from said observer's eyeball pass through the first surface and are reflected by the second surface and further reflected by the third surface, which is a reflecting surface having positive power, and the light rays reflected by said third surface are reflected by said first surface and pass through said second surface to reach said image display device.  
     
     
       2. An image display apparatus according to claim  1 , wherein the reflection at said first surface is total reflection. 
     
     
       3. An image display apparatus according to claim  1  or  2 , wherein said third surface is disposed such that light rays on an observer's visual axis which have been reflected by said second surface are tilted at approximately 30° toward said observer's eyeball by reflection at said third surface. 
     
     
       4. An image display apparatus according to claim  3 , which satisfies the following condition: 
       
         
           20°<θ 1< 45°  (1)  
         
       
       where θ 1  is a tilt angle of said light rays. 
     
     
       5. An image display apparatus according to claim  3 , which satisfies the following condition: 
       
         
           25°<θ 1< 40°  (1′)  
         
       
       where θ 1  is a tilt angle of said light rays. 
     
     
       6. An image display apparatus according to claim  1  or  2 , which satisfies the following condition: 
       
         
           30°<θ 2 <60°  (2)  
         
       
       where θ 2  is an angle between said first surface and said second surface. 
     
     
       7. An image display apparatus according to claim  1  or  2 , wherein internal reflection at said second surface is total reflection. 
     
     
       8. 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 having at least four optical surfaces, wherein a space formed by said at least four optical surfaces is filled with a medium having a refractive index larger than 1,  
       said at least four optical surfaces being defined as a first surface, a second surface, a third surface, and a fourth surface, respectively, in order in which light rays pass in backward ray tracing from said observer's eyeball to said image display device, and  
       said at least four optical surfaces being disposed such that light rays pass in backward ray tracing from said observer's eyeball pass through the first surface and are reflected by the second surface and further reflected by the third surface, which is a reflecting surface having positive power, and the light rays reflected by said third surface are reflected by said first surface and pass through the fourth surface to reach said image display device.  
     
     
       9. An image display apparatus according to claim  8 , wherein the reflection at said first surface is total reflection. 
     
     
       10. An image display apparatus according to claim  8  or  9 , wherein said third surface is disposed such that light rays on an observer's visual axis which have been reflected by said second surface are tilted at approximately 30° toward said observer's eyeball by reflection at said third surface. 
     
     
       11. An image display apparatus according to claim  10 , which satisfies the following condition: 
       
         
           20°<θ 1 <45°  (1)  
         
       
       where θ 1  is a tilt angle of said light rays. 
     
     
       12. An image display apparatus according to claim  10 , which satisfies the following condition: 
       
         
           25°<θ 1 <40°  (1′)  
         
       
       where θ 1  is a tilt angle of said light rays. 
     
     
       13. An image display apparatus according to claims  8  or  9 , which satisfies the following condition: 
       
         
           30°<θ 2 <60°  (2)  
         
       
       where θ 2  is an angle between said first surface and said second surface. 
     
     
       14. An image display apparatus according to claim  1 ,  2 ,  8  or  9 , wherein at least one optical boundary surface is disposed in an optical path of said optical system. 
     
     
       15. An image display apparatus according to claim  1 ,  2 ,  8  or  9 , further comprising means for positioning both said image display device said ocular optical system with respect to an observer's head. 
     
     
       16. An image display apparatus according to claim  1 ,  2 ,  8  or  9 , 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. 
     
     
       17. An image display apparatus according to claim  1 ,  2 ,  8  or  9 , further comprising means for supporting at least a pair of said image display apparatuses at a predetermined spacing. 
     
     
       18. An image display apparatus according to claim  1 ,  2 ,  8  or  9 , wherein said ocular optical system is used as an imaging optical system. 
     
     
       19. An ocular optical system disposed between an image plane and a pupil, 
       
         said optical system comprising a prism member having at least three surfaces including a first surface, a second surface, and a third surface, wherein a space formed by said at least three surfaces is filled with a medium having a refractive index larger than  1 ,  
       
       
         wherein said prism member is arranged such that light rays as traced from said image plane toward said pupil first pass through said second surface and are then reflected by said first surface and further reflected by said third surface, and the reflected light rays are reflected by said second surface and pass through said first surface, and/or such that light rays as traced from said pupil toward said image plane first pass through said first surface and are then reflected by said second surface and further reflected by said third surface, and the reflected light rays are reflected by said first surface and pass through said second surface, and  
       
       
         wherein at least one of said first surface, said second surface and said third surface is a curved surface. 
       
     
     
       20. An ocular optical system according to claim  19 , wherein said first surface is positioned to face opposite to said image plane. 
     
     
       21. An ocular optical system according to claim  19 , wherein said first surface has a curved surface configuration which gives a positive power to the light rays when reflected by said first surface. 
     
     
       22. An ocular optical system according to claim  19 , wherein said second surface has a curved surface configuration which gives a positive power to the light rays when reflected by said second surface. 
     
     
       23. An ocular optical system according to claim  19 , wherein said third surface has a curved surface configuration which gives a positive power to the light rays when reflected by said third surface. 
     
     
       24. An ocular optical system according to claim  19 ,  20 ,  21 ,  22  or  23 , wherein said prism member inverts the image formed on said image plane, upside down. 
     
     
       25. An ocular optical system according to claim  24 , wherein said first surface has a rotationally asymmetric curved surface configuration having an action by which decentration aberrations are corrected. 
     
     
       26. An ocular optical system according to claim  24 , wherein said third surface has a rotationally asymmetric curved surface configuration having an action by which decentration aberrations are corrected. 
     
     
       27. An ocular optical system according to claim  24 , wherein said first surface is formed from a spherical surface. 
     
     
       28. An ocular optical system according to claim  24 , wherein said second surface is formed from a spherical surface. 
     
     
       29. An ocular optical system according to claim  24 , wherein said third surface is formed from a spherical surface. 
     
     
       30. An ocular optical system according to claim  24 , wherein reflection at said first surface is total reflection. 
     
     
       31. An ocular optical system according to claim  24 , wherein reflection at said second surface is total reflection. 
     
     
       32. An ocular optical system according to claim  24 , wherein said prism member is arranged such that a spacing between said first surface and second surface gradually increases toward said third surface. 
     
     
       33. An ocular optical system according to claim  24 , which satisfies the following condition: 
       
         
           
               30 °<θ 
             2 
             < 60 ° 
           
         
       
       
         where θ 
         2  
         is an angle formed between said first surface and said second surface. 
       
     
     
       34. An ocular optical system according to claim  24 , further comprising a lens disposed between said prism member and said image plane. 
     
     
       35. An ocular optical system according to claim  34 , wherein said lens is cemented to said second surface of said prism member. 
     
     
       36. An ocular optical system according to claim  24 , wherein a field angle in a horizontal direction of said prism member is different from a field angle in a vertical direction thereof. 
     
     
       37. An ocular optical system according to claim  24 , wherein the field angle in the horizontal direction of said prism member is larger than the field angle in the vertical direction thereof. 
     
     
       38. An image- forming optical system which forms an image of an object,    
         said image - forming optical system comprising at least one prism member,    
       
         wherein said prism member has at least three optical surfaces, wherein a space formed by said at least three optical surfaces is filled with a medium having a refractive index larger than  1 , and said at least three optical surfaces are defined as a first surface, a second surface, and a third surface, respectively, in order of ray tracing from the object to an image plane,  
       
       
         said at least three optical surfaces being disposed such that light rays from said object pass through said first surface and are then reflected by said second surface and further reflected by said third surface, and the reflected light rays are reflected by said first surface and pass through said second surface to reach said image plane, and  
       
       
         wherein at least one of said first surface, said second surface and said third surface is formed from a curved surface to give a positive power to the light rays when reflected by said at least one surface. 
       
     
     
       39. An image- forming optical system according to claim  38 , wherein said first surface is positioned to face opposite to said image plane.   
     
     
       40. An image- forming optical system according to claim  38 , wherein said first surface has a curved surface configuration which gives a positive power to the light rays when reflected by said first surface.   
     
     
       41. An image- forming optical system according to claim  38 , wherein said second surface has a curved surface configuration which gives a positive power to the light rays when reflected by said second surface.   
     
     
       42. An image- forming optical system according to claim  38 , wherein said third surface has a curved surface configuration which gives a positive power to the light rays when reflected by said third surface.   
     
     
       43. An image- forming optical system according to claim  38 ,  39 ,  40 ,  41  or  42 , wherein reflection at least one of said first surface and second surface is total reflection.   
     
     
       44. An image- forming optical system according to claim  43 , wherein said first surface has a rotationally asymmetric curved surface configuration having an action by which decentration aberrations are corrected.   
     
     
       45. An image- forming optical system according to claim  43 , wherein said third surface has a rotationally asymmetric curved surface configuration having an action by which decentration aberrations are corrected.   
     
     
       46. An image- forming optical system according to claim  43 , wherein said first surface is formed from a spherical surface.   
     
     
       47. An image- forming optical system according to claim  43 , wherein said second surface is formed from a spherical surface.   
     
     
       48. An image- forming optical system according to claim  43 , wherein said third surface is formed from a spherical surface.   
     
     
       49. An image- forming optical system according to claim  43 , wherein said prism member is arranged such that a spacing between said first surface and said second surface gradually increases toward said third surface.   
     
     
       50. An image- forming optical system according to claim  43 , which satisfies the following condition:    
       
         
           30°<θ 2   < 60 °   
         
       
       
         where θ 
         2  
         is an angle formed between said first surface and said second surface. 
       
     
     
       51. An image- forming optical system according to claim  43 , further comprising a lens disposed between said prism member and said image plane.   
     
     
       52. An image- forming optical system according to claim  51 , wherein said lens is cemented to said second surface of said prism member.   
     
     
       53. An image- forming optical system according to claim  43 , wherein a field angle in a horizontal direction of said prism member is different from a field angle in a vertical direction thereof.   
     
     
       54. An image- forming optical system according to claim  43 , wherein the field angle in the horizontal direction of said prism member is larger than the field angle in the vertical direction thereof.   
     
     
       55. A camera apparatus according to claim  43 , wherein said image- forming optical system is disposed to perform image formation.   
     
     
       56. A camera apparatus according to claim  55 , wherein a photographic optical system and a finder optical system are disposed separately from each other. 
     
     
       57. A camera apparatus according to claim  56 , wherein said image- forming optical system is disposed in said finder optical system.   
     
     
       58. A camera apparatus according to claim  57 , wherein said finder optical system includes, in order from an object side thereof, said image- forming optical system; an image erecting optical system for erecting the object image formed by said image - forming optical system; and an ocular optical system for observing said object image.   
     
     
       59. An optical system disposed between an image plans and a pupil, 
       
         said optical system comprising at least one prism member,  
       
       
         said prism member having at least three reflecting surfaces that reflect a light beam in said prism member, said three reflecting surfaces being so arranged that optical paths intersect each other in said prism member,  
       
       
         wherein at least one of said at least three reflecting surfaces has a curved surface configuration. 
       
     
     
       60. An optical system according to claim  59 , wherein said at least three reflecting surfaces of said prism member are curved surfaces.