Abstract:
A picture display apparatus is provided in which not only reduction in weight and protruding amount is achieved but also aberration is small and wide-angle display can be inexpensively performed by providing a semitransparent reflecting surface. 
     A picture display apparatus of the present invention includes cholesteric liquid crystal for displaying a plane image, a fiber plate for converting a displayed plane image into a spherical image, and an eyepiece optical system having first and second spherical semitransparent reflecting surfaces and projecting a spherical image. A spherical image with its center of curvature in the vicinity of the pupil is reflected at the second and the first spherical semitransparent reflecting surfaces and is then directed to the viewer&#39;s pupil.

Description:
This application is based on applications Nos. H9-253111 and H10-210643 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a picture display apparatus, and more particularly, to a picture display apparatus designed so as to be mounted on the viewer&#39;s head or face. The present invention further relates to a camera requiring no complicated picture conversion processing. 
     2. Description of the Prior Art 
     For a head mounted display (HMD), reduction in overall weight and protruding amount of the apparatus is important in order to improve the mountability of the apparatus. A factor that decides the overall weight of the apparatus is the optical system layout. Among the optical systems that have hitherto been disclosed, examples of optical systems that can be reduced in protruding amounts of apparatus are shown in FIGS. 1 and 2. 
     FIRST CONVENTIONAL EXAMPLE 
     FIG. 1 shows an optical system disclosed in Japanese Laid-open Patent Application No. H7-175009. This optical system projects an image surface  100  far away through a semitransparent reflecting surface  102  and a semitransparent reflecting surface  101 . According to this arrangement, the size of the optical system can be reduced by repetitively reflecting the light between the image surface  100  and a viewer&#39;s pupil position  103 , so that the amount of frontward protrusion of the HMD from the viewer&#39;s head can be reduced. 
     SECOND CONVENTIONAL EXAMPLE 
     FIG. 2 shows an optical system disclosed in U.S. Reissued Pat. No. 27356. This optical system projects an image surface  104  far away through a semitransparent concave mirror  105  and a semitransparent plane mirror  106 . According to this arrangement, like the first conventional example, the size of the optical system can be reduced by repetitively reflecting the light between the image surface  104  and a viewer&#39;s pupil position  107 . 
     For an HMD, in addition to reduction in overall weight and protruding amount of the apparatus, provision of a large angle of view is important. Provision of a large angle of view enables display of more realistic pictures. However, in the first conventional example, since plane images are viewed being enlarged, correction of optical aberrations such as field curvature and distortion is limited, so that the angle of view cannot be widened. 
     In the second conventional example, since the image surface is a curved surface having its center on the side opposite to the pupil position, the angle of view cannot be widened. 
     In both of the two conventional examples, the pictures projected onto the viewer&#39;s pupil are plane images. However, viewers view more realistic pictures by viewing spherical images than by viewing plane images. 
     Another problem will be described. A picture display apparatus for viewing pictures taken from life has been disclosed and in this apparatus, a necessary range of a picture is cut out from the shooting range and then the cut out picture is viewed. However, in case a picture is viewed with a position different from the shooting center as the viewing center, it is necessary to convert image data since faithful picture reproduction cannot be performed by using the video signals of the shot picture as they are. Therefore, for example, it is necessary to perform image processing and this increases the price of the apparatus. 
     A conventional camera for shooting plane images also has problems. Even if plane images are continuously shot, it is impossible to obtain a 360-degree picture in which these images connect neatly. In a case where plane images shot by this type of camera are viewed by being displayed on a display apparatus, when a picture is viewed with a position different from the shooting center as the viewing center, the positional relationship among the objects in the picture changes. This will be described with reference to FIGS. 3 to  5 . 
     FIG. 3 is a schematic cross-sectional view of an optical system of a camera. Reference numeral  112  represents a taking lens. Point B 1  represents the principal point of the taking lens  112 . Reference numeral  111  represents an image shot surface comprising a plane. α 11  represents the shooting range of the camera. When a picture including objects  108 ,  109  and  110  is shot with the object  108  as the shooting center, the light rays from the objects are imaged on the image shot surface  111  as shown in the figure. 
     The angle between the straight lines connecting the objects and the principal point B 1  is θ 111  between the objects  108  and  109  and is θ 121  between the objects  109  and  110 . The distance between the objects shot on the image shot surface  111  is y 1  between objects  108   a  and  109   a  and is Y 2  between the objects  109   a  and  110   a . The focal length of the taking lens  112  is f. Here, the relationship between Y 1 , Y 2  and θ 111 , θ 121  is represented by these expressions. 
     
       
         Y 1 =f tanθ 111   (1) 
       
     
     
       
         Y 2 =f tan(θ 111 +θ 121 )−Y 1   (2) 
       
     
     Hereinafter, a picture viewed when a part of the shooting range α 11  is viewed with a picture display apparatus will be described with reference to FIGS. 4 and 5. FIGS. 4 and 5 are schematic cross-sectional views of the picture display apparatus. On a display device  113 , the picture on the image shot surface  111  which is horizontally and vertically flipped is displayed as it is. The viewer views the picture through an eyepiece  114 . Point B 2  represents the principal point of the taking lens. The focal length of the taking lens  114  is f same as that of the camera. 
     FIGS. 4 and 5 are schematic cross-sectional views of the optical system of the picture display apparatus when a range β 11  is viewed with the object  108   a  as the viewing center and when a range β 12  is viewed with the object  109   a  as the viewing center, respectively. 
     In FIG. 4, the viewer views objects  108   b ,  109   b  and  110   b . At this time, the angle between the straight lines connecting the viewed objects and the principal point B 2  of the taking optical system  114  is θ 112  between the objects  108   b  and  109   b  and is θ 122  between the objects  109   b  and  110   b . The relationship between θ 112 , θ 122  and y 1 , Y 2  is represented by these expressions. 
     
       
         θ 112 =tan −1 (y 1 /f)  (3) 
       
     
     
       
         θ 122 =tan −1 {(y 1 +y 2 )/f}−θ 112   (4) 
       
     
     Comparing the expressions (1) and (3) and the expressions (2) and (4), it is apparent that θ 112 =θ 111  and θ 122 =θ 121 . 
     In FIG. 5, the viewer views objects  108   c ,  109   c  and  110   c . At this time, the angle between the straight lines connecting the objects and the principal point B 2  of the taking optical system  114  is θ 113  between the objects  108   c  and  109   c  and is θ 123  between the objects  109   c  and  110   c . The relationship between θ 113 , θ 123  and Y 1 , Y 2  is represented by these expressions. 
      θ 113 =tan −1 (y 1 /f)  (5) 
     
       
         θ 123 =tan −1 (y 2 /f)  (6) 
       
     
     Comparing the expressions (1) and (5) and the expressions (2) and (6), it is apparent that θ 113 =θ 111  and θ 123 ≠θ 121 . Thus, when a picture is viewed with a position different from the shooting center as the viewing center (this occurs when the shooting range is larger than the display screen), the picture viewed by the viewer is not faithful reproduction of the shot picture. 
     In order to display faithful reproduction of shot pictures with conventional display apparatuses, it is necessary to perform complicated image processing when pictures are displayed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a picture display apparatus being lightweight, small in protruding amount and capable of inexpensively performing wide-angle display. 
     Another object of the present invention is to provide a picture display apparatus and a camera in which it is unnecessary to perform complicated picture conversion processing even when pictures are viewed with a position different from the shooting center as the viewing center. 
     To achieve the above-mentioned objects, a picture display apparatus of the present invention comprises: display means for displaying a spherical image; and an eyepiece optical system having first and second spherical semitransparent reflecting surfaces, the eyepiece optical system projecting the spherical image. 
     According to this arrangement, since the viewer views a spherical image displayed by the display means being enlarged through the eyepiece optical system, the viewer views a highly realistic picture with few aberrations. The display means comprises, for example, a display portion for displaying a plane image and a converting portion for converting a displayed plane image into a spherical image. 
     Moreover, a picture display apparatus of the present invention comprises: display means for deflection-scanning light in two directions to display a spherical image; and an eyepiece optical system having first and second surfaces, the eyepiece optical system projecting a spherical image. 
     According to this arrangement, high-definition pictures can be provided by forming pictures by scanning light from a light source. Moreover, since the viewer views a spherical image displayed by the display means being enlarged through the eyepiece optical system, the viewer views a highly realistic picture with few aberrations. 
     A camera of the present invention comprises: a taking optical system having first and second spherical semitransparent reflecting surfaces; converting means for converting a spherical image projected by the taking optical system into a plane image; and shooting means for shooting a converted plane image. 
     According to this arrangement, a spherical image with few aberrations is projected through the taking optical system. The spherical image is converted into a plane image through the converting means and the plane image is shot by the shooting means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which: 
     FIG. 1 is a cross-sectional view of the optical system of the first conventional example; 
     FIG. 2 is a cross-sectional view of the optical system of the second conventional example; 
     FIG. 3 shows the shooting angle of the conventional camera; 
     FIG. 4 shows the viewing angle of the conventional picture display apparatus (when no image processing is performed); 
     FIG. 5 shows the viewing angle of the conventional picture display apparatus (when no image processing is performed) when the viewing center is different from that of FIG. 4; 
     FIG. 6 is a cross-sectional view of an optical system of a picture display apparatus according to a first embodiment; 
     FIG. 7 is a cross-sectional view of an optical system of a picture display apparatus according to a second embodiment; 
     FIG. 8 is a cross-sectional view of an optical system of a picture display apparatus according to a third embodiment; 
     FIG. 9 is a cross-sectional view of an optical system of a picture display apparatus according to a fourth embodiment; 
     FIG. 10 is a cross-sectional view of an optical system of a camera according to a fifth embodiment; 
     FIG. 11 shows a shooting angle of the camera; 
     FIG. 12 shows a viewing angle of the picture display apparatus; 
     FIG. 13 shows a viewing angle of the picture display apparatus when the viewing center is different from that of FIG. 12; 
     FIG. 14 is a cross-sectional view of an optical system of a picture display apparatus according to a sixth embodiment; and 
     FIG. 15 is a cross-sectional view of an optical system of a picture display apparatus according to a seventh embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 
     &lt;First Embodiment&gt; 
     FIG. 6 is a cross-sectional view of an optical system of a picture display apparatus according to a first embodiment of the present invention. Reference numeral  1  represents cholesteric liquid crystal serving as a display portion. The light exiting from the cholesteric liquid crystal  1  is circularly polarized picture light. Reference numeral  3  represents a fiber plate serving as a spherical image converting portion. The fiber plate  3  has on the side of a viewer&#39;s pupil  5  a spherical surface having its center of curvature in the vicinity of the pupil  5 . On the spherical surface, a spherical semitransparent reflecting surface (first semitransparent reflecting surface)  3   a  is formed. The fiber plate  3  converts the pictures displayed by the cholesteric liquid crystal  1  into spherical images. 
     Reference numeral  4  represents cholesteric liquid crystal comprising a spherical surface (second semitransparent reflecting surface) having its center of curvature in the vicinity of the viewer&#39;s pupil  5 . The cholesteric liquid crystal  4  selectively transmits and reflects circularly polarized light according to the rotation direction of the circularly polarized light. The first semitransparent reflecting surface  3   a  and the second semitransparent reflecting surface constitute an eyepiece optical system. Reference numeral  6  represents a virtual image viewed by the pupil  5  through the eyepiece optical system. 
     The picture light of a plane image exiting from the cholesteric liquid crystal  1  is converted into picture light of a spherical image by the fiber plate  3 . The picture light is reflected at the cholesteric liquid crystal  4  without the circular polarization direction changed. Then, the picture light is reflected at the semitransparent reflecting surface  3   a  of the fiber plate  3 . At this time, the circular polarization direction is reversed. The picture light with its circular polarization direction reversed is then transmitted by the cholesteric liquid crystal  4  and supplied to the viewer&#39;s pupil  5 . The viewer views the virtual image  6 . 
     According to this arrangement, since the centers of curvature of the first semitransparent reflecting surface  3   a  and the second semitransparent reflecting surface are set in the vicinity of the pupil  5 , pictures with only spherical aberration can be provided to the viewer. Here it is preferable that the radius of curvature of the first semitransparent reflecting surface  3   a  is 1.5 or less times that of the second semitransparent reflecting surface  4 . With this arrangement, the diopter within the pupil  5  can be set at a finite distance. 
     &lt;Second Embodiment&gt; 
     FIG. 7 is a cross-sectional view of an optical system of a picture display apparatus according to a second embodiment of the present invention. The plane display portion of this embodiment comprises a liquid crystal display (LCD)  7 . The structure of the spherical image converting portion and the first and the second semitransparent reflecting surfaces is the same as that of the first embodiment. In the second embodiment, a quarter-wave plate  2  serving as a polarizing portion is formed between the LCD  7  and the fiber plate  3 . 
     The linearly polarized light exiting from the LCD  7  is converted into circular polarized light by the quarter-wave plate  2  and then converted into a spherical image by the fiber plate  3 . The fiber plate  3  of this embodiment is structured so that the incident light exits with its polarization condition maintained. That is, linearly polarized spherical image light exits from the fiber plate  3 . The order of travel of the light exiting from the fiber plate  3  will not be described because it is the same as that of the first embodiment. 
     &lt;Third Embodiment&gt; 
     FIG. 8 is a cross-sectional view of an optical system of a picture display apparatus according to a third embodiment of the present invention. Reference numeral  8  represents a polarizing plate serving as a selectively transmitting portion. The polarizing plate  8  is formed to be spherical on the pupil  5  side spherical surface of a fiber plate  3  and transmits linearly polarized light of a specific direction. A quarter-wave plate  2  serving as a polarizing portion of this picture display apparatus is formed to be spherical on the pupil  5  side spherical surface of the polarizing plate  8 . A first semitransparent reflecting surface  2   a  is formed to be spherical on the pupil  5  side spherical surface of the quarter-wave plate  2 . The structure of other portions is the same as that of the second embodiment. 
     The picture light of a plane image exiting from the LCD  7  is converted into picture light of a spherical image by the fiber plate  3 . The fiber plate  3  of this embodiment does not maintain the polarization condition of the incident light. The polarizing plate  8  transmits linearly polarized light of the light exiting from the fiber plate  3 . The transmitted light is converted into circularly polarized light by the quarter-wave plate  2 . The order of travel of the light exiting from the quarter-wave plate  2  will not be described because it is the same as that of the first embodiment. 
     &lt;Fourth Embodiment&gt; 
     FIG. 9 is a cross-sectional view of an optical system of a picture display apparatus according to a fourth embodiment of the present invention. Reference numeral  1  represents cholesteric liquid crystal serving as a display portion. The light exiting from the cholesteric liquid crystal  1  is circularly polarized picture light. Reference numeral  3  represents a fiber plate having on the side of a viewer&#39;s pupil  5  a spherical semitransparent reflecting surface  3   a  (first semitransparent reflecting surface) with its center of curvature in the vicinity of the pupil  5 . The fiber plate  3  converts the plane images displayed by the cholesteric liquid crystal  1  into spherical images. 
     Reference numeral  2  represents a quarter-wave plate comprising a spherical surface with its center of curvature in the vicinity of the viewer&#39;s pupil  5 . The quarter-wave plate  2  converts linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. Reference numeral  8  represents a polarizing plate serving as a selectively transmitting portion for selectively transmitting and reflecting linearly polarized light different in direction by 90 degrees. That is, the surface of the polarizing plate  8  which is in contact with the quarter-wave plate  2  serves as a second semitransparent reflecting surface  8   a . The first semitransparent reflecting surface  3   a  and the second semitransparent reflecting surface  8   a  constitute an eyepiece optical system. Reference numeral  6  represents a virtual image viewed by the viewer. 
     The picture light of a plane image exiting from the cholesteric liquid crystal  1  is converted into picture light of a spherical image by the fiber plate  3 , and is then converted from circular polarized light into linearly polarized light by the quarter-wave plate  2 . The linearly polarized light is reflected at the second semitransparent reflecting surface  8   a . The picture light again converted into circularly polarized light by the quarter-wave plate  2  is reflected at the first semitransparent reflecting surface  3   a . At this time, the circular polarization direction is reversed. The picture light with its circular polarization direction reversed is converted into linearly polarized light (linearly polarized light different in direction from the previous linearly polarized light) by the quarter-wave plate  2 , and is then transmitted by the polarizing plate  8  to be made incident on the viewer&#39;s pupil  5 . The viewer views the virtual image  6 . 
     In this picture display apparatus, like in the first embodiment, it is preferable that the radius of curvature of the first semitransparent reflecting surface  3   a  is 1.5 or less times that of the second semitransparent reflecting surface  8   a . With this arrangement, the diopter within the pupil  5  can be set at a finite distance. 
     While the plane display portion and the fiber plate  3  for converting plane images into spherical images are used in the first to the fourth embodiments, a spherical display portion may be provided without the provision of the converting portion such as the fiber plate. For example, the use of a spherical liquid crystal display (LCD) makes it unnecessary to provide a converting portion such as a fiber plate. 
     &lt;Fifth Embodiment&gt; 
     FIG. 10 is a cross-sectional view of an optical system of a camera according to a fifth embodiment of the present invention. Reference numeral  9  represents an entrance pupil. Reference numeral  8  represents a polarizing plate for selectively transmitting and reflecting linearly polarized light different in direction by 90 degrees. The polarizing plate  8  comprises a spherical surface with its center of curvature in the vicinity of the entrance pupil  9 . Reference numeral  2  represents a quarter—wave plate comprising a spherical surface for converting circularly polarized light into linearly polarized light and linearly polarized light into circularly polarized light. On the side surface of the quarter-wave plate  2  on the side opposite to the entrance pupil  9 , a first semitransparent reflecting surface  2   a  is formed. 
     Reference numeral  4  represents cholesteric liquid crystal (second semitransparent reflecting surface) for selectively reflecting and transmitting circularly polarized light. The cholesteric liquid crystal  4  comprises a spherical surface with its center of curvature in the vicinity of the entrance pupil  9 . The first semitransparent reflecting surface  2   a  and the second semitransparent reflecting surface  4  constitute a taking optical system. Reference numeral  3  represents a fiber plate for converting spherical images into plane images. Reference numeral  10  represents a photoelectric converter (CCD). 
     Of subject light passing through the entrance pupil  9 , only linearly polarized light of a specific direction is transmitted by the polarizing plate  8 . The light transmitted by the polarizing plate  8  is converted into circularly polarized light by the quarter-wave plate  2  and is reflected at the cholesteric liquid crystal  4  without the circularly polarization direction changed. Then, the light is reflected at the first semitransparent reflecting surface  2   a . Since the polarization direction is reversed at this time, the light is transmitted by the cholesteric liquid crystal  4 . The light transmitted by the cholesteric liquid crystal  4  is converted from a spherical image into a plane image by the fiber plate  3  and is supplied to the CCD  10 . The CCD  10  shoots the supplied plane image. The entrance pupil  9  side spherical surface  3   b  of the fiber plate  3  serves as the image formed surface. 
     The relationship between the shooting angle and the viewing angle when pictures taken by the camera of the fifth embodiment are viewed with the picture display apparatuses of the first to the fourth embodiments will hereinafter be described. 
     FIG. 11 shows the shooting angle of the camera. The optical system of the camera of the fifth embodiment is simplified so that only the quarter-wave plate  2  and the image formed surface  3   b  are shown. Point A represents the principal point of the taking optical system. Assume that objects  11 ,  12  and  13  are simultaneously shot with the object  11  as the shooting center. At this time, the objects are projected onto the image formed surface  3   b  as objects  11   a ,  12   a  and  13   a , respectively. α 1  represents the shooting range. The angle between the straight lines connecting the objects  11 ,  12  and  13  and the principal point A is all between the objects  11  and  12  and is θ 21  between the objects  12  and  13 . The objects are imaged on the image formed surface  3   b  with this angle relationship maintained. 
     This camera has storing means (not shown) for storing shot pictures and picture range selecting means (not shown) for selecting which range of a stored picture is outputted based on a signal from the picture display apparatus. The picture range selecting means is enabled when the display range of the picture display apparatus is smaller than the shooting range of the camera or a stored wide-range (for example, 360-degree) picture having been shot previously. 
     The shooting angle when a picture shot as described above is viewed, for example, with the picture display apparatus of the first embodiment will be described. In the camera of the fifth embodiment, a spherical image on the image formed surface  3   b  shown in FIG. 6 is converted into a plane image and captured by the CCD  10 . 
     This picture is displayed being horizontally and vertically flipped on the display means  1  of the picture display apparatus of the first embodiment, and then, converted into a spherical image (the same as the spherical image before the image capture by the CCD  10  in the camera except that this spherical image is horizontally and vertically flipped) and picture light is outputted from the semitransparent reflecting surface  3   a . The process of conversion into plane images is not shown in FIG.  11  and FIGS. 12 and 13 which are schematic cross-sectional views of the optical system of the picture display apparatus. 
     FIG. 12 shows the viewing angle when a range β 1  is viewed with the object lla on the image formed surface  3   b  of FIG. 11 as the viewing center. FIG. 13 shows the shooting angle when a range β 2  is viewed with the object  12   a  on the image formed surface  3   b  of FIG. 12 as the viewing center. 
     In FIG. 12, when the viewer views a spherical image through the eyepiece optical system, virtual image objects  11   b ,  12   b  and  13   b  are viewed. The angle between the straight lines connecting the viewed virtual image objects and the pupil  5  is θ 12  between the objects  11   b  and  12   b  and is θ 22  between the objects  12   b  and  13   b . Comparing with FIG. 11, since the angles between the objects on the display surface  3   a  and on the image formed surface  3   b  are the same, it is apparent that θ 12 =θ 11  and θ 22 =θ 21 . 
     As shown in FIG. 13, when the viewer views a spherical surface with the object  12   a  as the viewing center, virtual image objects  11   c ,  12   c  and  13   c  are viewed. Deciding the angles between the viewed objects similarly to FIG. 12, the angle is θ 13  between the objects  11   c  and  12   c  and is θ 23  between the objects  12   c  and  13   c . Comparing with FIG. 11, like the case of FIG. 12, since the angles between the objects on the display surface  3   a  and on the image formed surface  3   b  are the same, it is apparent that θ 13 =θ 11  and θ 23 =θ 21  . 
     While the viewing angle when pictures shot by the camera are viewed with the picture display apparatus of the first embodiment has been described above, the same applies to the viewing angles when pictures are viewed with the picture display apparatuses of the second to the fourth embodiments because the picture display apparatuses of the second to the fourth embodiments have essentially the same structure as that of the first embodiment. Therefore, no detailed description will be given as to the shooting angles when pictures are viewed with these picture display apparatuses. 
     As shown in FIGS. 12 and 13, when pictures shot by use of the camera of the fifth embodiment are viewed with the picture display apparatuses of the first to the fourth embodiments, the positional relationship among the objects never changes even when the pictures are viewed with a position different from the shooting center of the camera as the viewing center. 
     While picture display apparatuses whose display portion comprises cholesteric liquid crystal or a liquid crystal display (LCD) have been described as the first to the fourth embodiments, the display portion of the picture display apparatus achieving the present invention is not limited thereto. For example, the display portion may comprise a point light source and scanning means. Picture display apparatuses of the present invention having a display portion comprising a point light source and scanning means will hereinafter be described as sixth and seventh embodiments. 
     &lt;Sixth Embodiment&gt; 
     FIG. 14 is a cross-sectional view of an optical system of a picture display apparatus according to the sixth embodiment of the present invention viewed from a side. C shows a part of the picture display apparatus viewed from above. Reference numeral  18  represents a main scanning mirror for scanning incident light in the horizontal direction. As shown in C viewed from above, light emitted by a light source  14  modulated by a video signal is condensed by a condenser lens  17  and made incident on the main scanning mirror  18 . Between the light source  14  and the condenser lens  17 , a polarizing plate  15  and a quarter-wave plate  16  are disposed. By these elements, light from the light source  14  is polarized into left-handed circularly polarized light and is made incident on the main scanning mirror  18 . 
     Reference numeral  19  represents a sub scanning mirror for scanning light from the main scanning mirror  18  in the vertical direction. Reference numeral  4  is cholesteric liquid crystal comprising a spherical surface (first surface) with its center of curvature in the vicinity of a viewer&#39;s pupil  5 . The cholesteric liquid crystal  4  selectively transmits and reflects circularly polarized light according to the rotation direction of the circularly polarized light. In this embodiment, cholesteric liquid crystal is used that transmits right-handed circularly polarized light and reflects left-handed circularly polarized light. Reference numeral  21  represents a concave mirror for projecting virtual images onto the viewer&#39;s pupil  5 . The concave mirror  21  comprises a spherical surface (second surface) with its center of curvature in the vicinity of the viewer&#39;s pupil  5 . The cholesteric liquid crystal  4  and the concave mirror  21  constitute an eyepiece optical system. Reference numeral  20  is a half mirror for reflecting light from the sub scanning mirror  19  toward the cholesteric liquid crystal  4  and for transmitting light from the direction of the cholesteric liquid crystal  4  and supplying it to the viewer&#39;s pupil  5 . The main scanning mirror  18  is disposed in a position substantially conjugate with the viewer&#39;s pupil  5  with respect to the concave mirror  21 . 
     Picture light of left-handed circularly polarized light scanned by the scanning means comprising the two scanning mirrors  18  and  19  is reflected at the half mirror  20  into right-handed circularly polarized light, is transmitted by the cholesteric liquid crystal  4  and is imaged to be spherical in the vicinity of the concave mirror  21 . The spherical image is reflected at the concave mirror  21  into left-handed circularly polarized light, is reflected at the cholesteric liquid crystal  4  (the polarization direction does not change at this time) and is again reflected at the concave mirror  21 . At this time, the light is converted into right-handed circularly polarized light, is transmitted by the cholesteric liquid crystal  4  and is further transmitted by the half mirror  20  to be directed to the viewer&#39;s pupil  5 . By the supplied light, the viewer views a virtual image. 
     &lt;Seventh Embodiment&gt; 
     FIG. 15 is a cross-sectional view of an optical system of a picture display apparatus according to the seventh embodiment of the present invention viewed from a side. C shows a part of the picture display apparatus viewed from above. Reference numeral  23  represents a quarter-wave plate. Reference numeral  24  represents a polarizing plate for transmitting only specific linearly polarized light. Reference numeral  25  represents a spherical screen for scattering incident light. These elements each comprise a spherical surface with its center of curvature in the vicinity of the viewer&#39;s pupil  5 . On the cholesteric liquid crystal  4  side surface of the quarter-wave plate  23 , a semitransparent reflecting surface (second surface)  22  is formed. As the polarizing plate  24 , one is used that is effective only for light from the direction of the screen  25 . The main scanning mirror  18  is disposed in a position substantially optically equivalent to the center of curvature of the screen  25  (that is, in a position substantially conjugate with the viewer&#39;s pupil  5 ). The structure of other portions is the same as that of the sixth embodiment. 
     Picture light of left-handed circularly polarized light scanned by the scanning means comprising the two scanning mirrors  18  and  19  is reflected at the half mirror  20  into right-handed circular polarized light, is transmitted by the cholesteric liquid crystal  4 , the quarter-wave plate  23  including the semitransparent reflecting surface  22  and the polarizing plate  24  and is imaged on the spherical screen  25 . The light of the spherical image imaged on the spherical screen  25  is scattered, and only specific linearly polarized light thereof is transmitted by the polarizing plate  24  and is converted into left-handed circular polarized light by the quarter-wave plate  23 . Then, the light is reflected at the cholesteric liquid crystal  4  (at this time, the polarization direction does not change) and is then reflected at the semitransparent reflecting surface  22 . At this time, the light is converted into right-handed circularly polarized light, is transmitted by the cholesteric liquid crystal  4  and is further transmitted by the half mirror  20  to be directed to the viewer&#39;s pupil. By the supplied light, the viewer views a virtual image. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.