Prism optical element, image observation apparatus and image display apparatus

Abstract

An extremely compact prism optical element, image observation apparatus and image display apparatus which are capable of providing an observation image that is clear and has minimal aberration and minimal distortion even at a wide field angle. Light rays emitted from an image display device ( 7 ) enter an ocular optical system ( 12 ) through a fourth surface ( 6 ) and are totally reflected toward an observer's pupil ( 1 ) by a third surface ( 5 ). The reflected light rays are reflected by a first surface ( 3 ) disposed immediately in front of the observer's pupil ( 1 ) and then reflected toward the observer's pupil ( 1 ) by a second surface ( 4 ). The reflected light rays pass through the first surface ( 3 ) and are projected into an observer's eyeball ( 15 ) with the observer's iris position as an exit pupil ( 1 ). When an external-scene image is observed, light rays from an object point in,the external scene enter the ocular optical system ( 12 ) through the third surface ( 5 ), pass through the first surface ( 3 ) and are projected into the observer's eyeball ( 15 ). Assuming that the angle of internal reflection of an arbitrary light ray at the third surface ( 5 ) is θ r3 , the ocular optical system ( 12 ) satisfies the condition of sin −1 (1/n d )≦θ r3 ≦60°, where n d is the refractive index for the spectral d-line of the medium of the ocular optical system ( 12 ).

1 . A prism optical element comprising a plurality of surfaces facing each other across a medium having a refractive index (n) larger than 1 (n>1), wherein said plurality of surfaces include a first surface having both a transmitting action through which light rays enter said prism optical element or exit therefrom and a reflecting action by which light rays are internally reflected in said prism optical element; 
 a second surface disposed to face said first surface across said medium and having a reflecting action by which light rays are internally reflected in said prism optical element;    a third surface disposed substantially close to said second surface to face said first surface across said medium and having a reflecting action by which light rays are internally reflected in said prism optical element; and    a fourth surface having such a transmitting action that when said first surface has an action through which light rays enter said prism optical element, said fourth surface has an action through which light rays exit from said prism optical element, whereas, when said first surface has an action through which light rays exit from said prism optical element, said fourth surface has an action through which light rays enter said prism optical element, and wherein the following condition is satisfied:    sin −1 (1/ n   d )≦θ r3 ≦60°  (1)    where n d  is a refractive index for the spectral d-line of said medium, and θ r3  is an angle of internal reflection of an arbitrary light ray at said third surface.    
     
     
         2 . A prism optical element according to  claim 1 , which satisfies the following condition:  
       sin −1 (1/ n   d )≦θ r3 ≦50°  (2)  
     
     
         3 . A prism optical element according to  claim 1 , wherein reflection at said first surface is total reflection.  
     
     
         4 . A prism optical element according to  claim 1 , wherein the refractive index (n) of said 0 medium is larger than 1.3 (n>1.3).  
     
     
         5 . A prism optical element according to  claim 1 , wherein at least one of surfaces constituting said prism optical element is a plane surface.  
     
     
         6 . An observation optical system comprising the prism optical element according to  claim 1 , said prism optical element being disposed in an observation optical system unit.  
     
     
         7 . An observation optical system according to  claim 6 , wherein said prism optical element is disposed in an objective lens.  
     
     
         8 . A camera finder optical system comprising the observation optical system of  claim 6 , wherein said prism optical element is disposed in image-erecting means disposed behind an objective lens to erect an object image formed by said objective lens.  
     
     
         9 . A camera finder optical system according to  claim 8 , wherein said prism optical element has an ocular lens action in addition to an image erecting action.  
     
     
         10 . A head-mounted image display apparatus comprising: 
 the prism optical element according to  claim 1;     image forming means disposed to face said fourth surface of said prism optical element; and    a retaining member that retains both said prism optical element and said image forming means on an observer's face wherein a bundle of light rays emitted from said image forming means enters said prism optical element through said fourth surface and passes sequentially along an optical path in said prism optical element such that the light rays are reflected successively by said third surface, said first surface and said second surface and exit from said prism optical element through said first surface.    
     
     
         11 . An image observation apparatus comprising image forming means and an ocular optical system having an action by which an image formed by said image forming means is led to an eyeball of an observer, 
 wherein said ocular optical system includes a prism member having at least three surfaces, wherein a space between said at least three surfaces is filled with a single medium having a refractive index (n) larger than 1 (n>1),    said prism member having an action by which light rays emitted from said image forming means are internally reflected at least three times, wherein at least two of the at least three internal reflections are total reflections, and    wherein at least one of the at least two total reflections is performed by a surface disposed on a side of said single medium that is closer to said observer, said surface being curved so as to correct aberrations produced by the internal reflections in said prism member, and    wherein at least two of the at least three surfaces of said prism member are disposed to face each other such that an external scene can be observed through said at least two surfaces, and that a distortion produced when the external scene is observed through said single medium is minimized.    
     
     
         12 - 32 . (canceled)  
     
     
         33 . An image observation apparatus according to  claim 10 , further comprising positioning means for positioning said image forming means and said ocular optical system with respect to an observer's head.  
     
     
         34 . An image observation apparatus according to  claim 10 , further comprising support means for supporting at least a pair of said image observation apparatuses at a predetermined spacing.  
     
     
         35 . A prism optical element or prism member according to  claim 1 , wherein said second surface and said third surface act as different surfaces in terms of optical action but are formed structurally from a single surface.  
     
     
         36 . A prism optical element or prism member according to  claim 35 , wherein said single surface constituting said second and third surfaces is arranged such that a region of said surface closer to said fourth surface acts as said third surface, and a region of said surface remote from said fourth surface acts as said second surface.  
     
     
         37 . A prism optical element or prism member according to  claim 36 , wherein said single surface constituting said second and third surfaces is arranged such that a central region of said surface acts as both said second and third surfaces.  
     
     
         38 . An image display apparatus comprising an image display device and an ocular optical system for leading an image formed by said image display device to an eyeball of an observer such that said image can be observed as a virtual image, 
 wherein said ocular optical system includes:    a decentered prism in which a space formed by at least two surfaces is filled with a medium having a refractive index larger than 1, said at least two surfaces including a first surface positioned immediately in front of the observer's eyeball, and a second surface which is a reflecting surface facing said first surface, at least one of said at least two surfaces being a curved surface decentered or tilted with respect to an observer's visual axis, and    aberration correcting means disposed outside said second surface to correct aberrations due to decentration produced by said first and second surfaces with respect to light from an external scene.    
     
     
         39 . An image display apparatus according to  claim 38 , wherein said aberration correcting means comprises a Fresnel lens.  
     
     
         40 . An image display apparatus according to  claim 39 , wherein a center of an annular zone of said Fresnel lens lies in a plane containing an optical path of an axial principal ray from said image display device, and said Fresnel lens is decentered perpendicularly to the observer's visual axis in the plane containing the optical path of the axial principal ray.  
     
     
         41 . An image display apparatus according to  claim 39 , wherein a center of an annular zone of said Fresnel lens lies in a plane containing an optical path of an axial principal ray from said image display device, and said Fresnel lens is tilted with respect to the observer's visual axis so as to extend along a surface configuration of said second surface.  
     
     
         42 . An image display apparatus according to  claim 38 , wherein said aberration correcting means comprises a diffractive optical element.  
     
     
         43 . An image display apparatus according to  claim 38 , wherein said aberration correcting means comprises a holographic optical element.  
     
     
         44 . An image display apparatus comprising an image display device and an ocular optical system for leading an image formed by said image display device to an eyeball of an observer such that said image can be observed as a virtual image, 
 wherein said ocular optical system includes a decentered prism in which a space formed by at least three surfaces is filled with a medium having a refractive index larger than 1;    said at least three surfaces including:    a refracting and internally reflecting surface positioned immediately in front of said observer's eyeball;    an outside world-side internally reflecting surface disposed on an outside world side of said ocular optical system to face said refracting and internally reflecting surface; and    a refracting surface through which a bundle of light rays emitted from said image display device enters said decentered prism,    wherein at least one of said at least three surfaces is decentered or tilted with respect to an observer's visual axis, and said at least three surfaces are arranged to perform at least three internal reflections,    said ocular optical system further includes a second optical element that cancels a power produced by said refracting and internally reflecting surface, which is positioned immediately in front of said observer's eyeball, and said outside world-side internally reflecting surface with respect to external light when an external scene is observed through said two surfaces,    said second optical element being disposed on an outside world side of said outside world-side internally reflecting surface.    
     
     
         45 . An image display apparatus according to  claim 44 , wherein said ocular optical system comprises a decentered prism in which a space formed by four surfaces is filled with a medium having a refractive index larger than 1, 
 said four surfaces including    a first surface positioned on an observer's eyeball side of said ocular optical system and serving as both refracting and reflecting surfaces,    a second surface which is a reflecting surface disposed to face said first surface;    a third surface which is a reflecting surface disposed to face said first surface at a position adjacent to said second surface; and    a fourth surface which is a refracting surface closest to said image display device,    wherein at least one of said four surfaces is decentered or tilted with respect to the observer's visual axis.    
     
     
         46 . An image display apparatus according to  claim 45 , wherein at least one second optical element is disposed on an outside world side of said second or third surface so that an external scene can be observed through said first surface, said second surface and said second optical element or through said first surface, said third surface and said second optical element.  
     
     
         47 . An image display apparatus according to  claim 46 , wherein said second optical element simultaneously cancels a composite power of said first and second surfaces and a composite power of said first and third surfaces with respect to light from the external scene.  
     
     
         48 . An image display apparatus according to claims  38  or  44 , further comprising positioning means for positioning said image display device and said ocular optical system with respect to an observer's head.  
     
     
         49 . An image display apparatus according to claims  38  or  44 , further comprising support means for supporting said image display device and said ocular optical system with respect to an observer's head such that said apparatus can be mounted on the observer's head.  
     
     
         50 . An image display apparatus according to claims  38  or  44 , further comprising support means for supporting at least a pair of said image display apparatuses at a predetermined spacing.  
     
     
         51 . An image display apparatus according to claims  38  or  44 , wherein said ocular optical system is used as an image-forming optical system.  
     
     
         52 . An optical system comprising: 
 a decentered prism having at least two surfaces, wherein a space formed by said at least two surfaces is filled with a medium having a refractive index larger than 1; and    aberration correcting means provided at a position separate from said decentered prism;    wherein at least one of said at least two surfaces is a curved surface decentered or tilted with respect to a predetermined axis, and    wherein said aberration correcting means is provided so that light that has passed through said aberration correcting means passes through said decentered prism.    
     
     
         53 . An optical system comprising: 
 a decentered prism 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; and    a second optical element provided at a position separate from said decentered prism;    wherein at least one of said at least three surfaces is a curved surface decentered or tilted with respect to a predetermined axis;    said at least three surfaces including a first surface and a second surface;    said second surface being positioned closest to said second optical element;    said first surface being positioned to face said second optical element across said second surface; and    wherein said second optical element is provided so that light that has passed through said second optical element passes through said decentered prism, and    said second optical element cancels a power produced by said second surface.