Patent Publication Number: US-2023139134-A1

Title: Virtual image display apparatus

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-177167, filed Oct. 29, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a virtual image display apparatus that guides imaging light to a pupil of a user by an optical system including a mirror formed by an imaging light generating unit or the like to enable observation of a virtual image. 
     2. Related Art 
     A known virtual image display apparatus that is applicable to a head-mounted display (HMD) includes three reflection surfaces and guides imaging light to a pupil of a user (JP-A-2020-20857). 
     However, in the eccentric optical system as described in JP-A-2020-20857, it is not easy to remove all distortion including trapezoidal distortion, and the occurring distortion needs to be electrically corrected, for example. However, this increases the circuit size and the power consumption. That is, a large load may be applied to the correction circuit side. 
     SUMMARY 
     A virtual image display apparatus according to an aspect of the present disclosure includes an imaging light emitting unit that emits an imaging light, a first mirror that reflects the imaging light from the imaging light emitting unit, an optical member that includes a reflecting portion reflecting the imaging light reflected by the first mirror, and a second mirror that reflects the imaging light reflected by the reflecting portion toward a position of an exit pupil, wherein a distance from the imaging light emitting unit to the first mirror is shorter than a distance from the position of the exit pupil to the second mirror, and a first angle between by the imaging light incident on the second mirror and the imaging light reflected by the second mirror is greater than 0° and 45° or less. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side cross-sectional view illustrating a virtual image display apparatus according to a first embodiment. 
         FIG.  2    is a front view for describing the virtual image display apparatus. 
         FIG.  3    is a side cross-sectional view for describing the optical structure and the like of the virtual image display apparatus. 
         FIG.  4    is a perspective view for describing the optical structure and the like of the virtual image display apparatus. 
         FIG.  5    is a side cross-sectional view for describing the shape of a second mirror of the virtual image display apparatus. 
         FIG.  6    is a plane cross-sectional view for describing the shape of a second mirror of the virtual image display apparatus. 
         FIG.  7    is a side cross-sectional view for describing the arrangement relationship of the portions of the virtual image display apparatus. 
         FIG.  8    is a conceptual diagram illustrating the arrangement of the members extracted from  FIG.  7   . 
         FIG.  9    is a conceptual diagram for describing a state of distortion aberration. 
         FIG.  10    is a graph showing resolution. 
         FIG.  11    is a side cross-sectional view for describing the optical structure and the like of a virtual image display apparatus according to a second embodiment. 
         FIG.  12    is a diagram for describing a state of distortion aberration. 
         FIG.  13    is a graph showing the relationship between a first angle and angle of view. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
     Next, a virtual image display apparatus according to the first embodiment of the present disclosure will be described with reference to drawings. 
     In  FIGS.  1  to  3   , X, Y, and Z represent a Cartesian coordinate system. The X direction corresponds to the lateral direction in which the eyes of a user US wearing a virtual image display apparatus  100  are aligned. The Y direction corresponds to the upward direction orthogonal to the lateral direction in which the eyes of the user US are aligned and also corresponds to the vertical direction when the user US wears the virtual image display apparatus  100  at a predetermined position (normal wearing position). Also, the Z direction corresponds to the forward or front direction from the perspective of the user US and also corresponds to the horizontal direction when the user US wears the virtual image display apparatus  100  at a predetermined position (normal wearing position). 
     The illustrated virtual image display apparatus  100  is a head-mounted display and allows the user US to perceive images as virtual images. The virtual image display apparatus  100  includes a display device  11 , which is an imaging light emitting unit, and a projection optical system  30 . The projection optical system  30  includes a lens member  12 , a first mirror  21 , a refractive reflective optical member  22 , and a second mirror  23 . Here, the lens member  12  is a prismatic member (see  FIG.  3   ) including aspheric refractive portion  12   a  and  12   b , the first mirror  21  is a mirror member including a reflecting portion (mirror portion)  21   r , and the second mirror  23  is a mirror member (see  FIG.  3   ) including a reflecting portion (mirror portion)  23   r . The refractive reflective optical member  22  is an optical member (see  FIG.  3   ) including a refractive member  22   b  and a mirror portion (reflecting portion)  22   r . The display device  11 , the lens member  12 , and the refractive reflective optical member  22  are fixed together, supported by a body member  81  of a frame  80 . Further, as illustrated in  FIGS.  1  and  2   , the first mirror  21  and the second mirror  23  constitute an appearance member  50  and are supported by the body member  81  of the frame  80  on the upper portion and the side portion. The appearance member  50  is disposed in a state in which it is positioned more outward from or to the external side of the display device  11  and the refractive reflective optical member  22  relative to both. The appearance member  50  has an outline shaped like eyeglasses and has a convex outwardly curved shape covering the eyes of the user US. Note that in  FIG.  1   , only the virtual image display apparatus  100  for the right eye is illustrated, but, as illustrated in  FIG.  2   , the virtual image display apparatus  100  for the left eye has the same structure, and a virtual image display apparatus having an appearance like eyeglasses as a whole is formed by combining virtual image display apparatuses for both eyes. Note that regarding the virtual image display apparatus for both eyes, either the portion for the right eye or the left eye may be omitted to form a single-eye head-mounted display. In describing an overview of an optical path, imaging light GL emitted from the display device  11  passes through the lens member  12 , is reflected by the first mirror  21 , and is incident on the refractive reflective optical member  22 . The imaging light GL incident on the refractive reflective optical member  22  is refracted and also reflected by the refractive reflective optical member  22  and emitted to the outside of the refractive reflective optical member  22 . The imaging light GL emitted from the refractive reflective optical member  22  is reflected by the second mirror  23  of the transmissive type and incident on a position of an exit pupil EP. 
     The frame  80  has a structure similar to that of eyeglasses, and includes a sidepiece portion  82  connected to a lateral end portion of the body member  81 , and a nose pad  83  at a tip of a metal fitting extending from the center of the body member  81 . 
     With reference to  FIG.  3   , the display device  11  is an image forming unit and is disposed on the upper side or the +Y side of the projection optical system  30  corresponding to a head side of the user US. The display device (image forming unit)  11  is a self-luminous type display element typified by, for example, an organic electro-luminescence (organic EL), an inorganic EL, an LED array, an organic LED, a laser array, a quantum dot emission type element, and the like, and forms a still image or a moving image in color on a two-dimensional display unit  11   a . The display device  11  is driven by a drive control circuit (not illustrated) and performs a display operation. When an organic EL display is used as the display device  11 , the display device  11  is configured to includes an organic EL control unit. When a quantum dot display is used as the display device  11 , the display device  11  is configured to emit green or red color by causing light of a blue light emitting diode (LED) to pass through a quantum dot film. The display device  11  is not limited to a self-luminous display element, and may be constituted by an LCD or the other light modulating element, and may form an image by illuminating the light modulating element with a light source such as a backlight. As the display device  11 , a liquid crystal on silicon (LCOS, LCoS is a trade name), a digital micromirror device, and the like may be used instead of the LCD. 
     The projection optical system  30  is a non-coaxial optical system or an eccentric optical system on the assumption that oblique incidence is used. An eccentric direction of the projection optical system  30  is defined by the arrangement of the lens member  12 , the first mirror  21 , the refractive reflective optical member  22 , and the like. Specifically, the lens member  12 , the first mirror  21 , the refractive reflective optical member  22 , and the second mirror  23  have the eccentric direction set within a YZ plane. In other words, an optical axis AX passing through the lens member  12 , the first mirror  21 , the refractive reflective optical member  22 , and the second mirror  23  is disposed along a plane that intersects the lateral direction in which a pair of pupils EY of the user US are aligned, i.e., the X direction, and extends in a substantially vertical direction and, more specifically, is disposed along the YZ plane that is orthogonal to the X direction and extends in the vertical direction. The optical axis AX is disposed along the vertical YZ plane, and thus an angle of view in the lateral direction is easily increased. When a plane including the optical axis AX is inclined in a clockwise direction or a counterclockwise direction (i.e., left or right) around the Z axis by a few 10°, an influence on the angle of view is not greatly increased with the optical axis AX extending in the substantially vertical direction. Further, the first mirror  21  is disposed on the upper side or the +Y side of the refractive reflective optical member  22  corresponding to the head side of the user US, and the refractive reflective optical member  22  is disposed on the upper side or the +Y side of the second mirror  23  corresponding to the head side of the user US. Herein, the upper side or the +Y side is considered with reference to an intersection or a point of contact between the lens member  12 , the first mirror  21 , the refractive reflective optical member  22 , and the second mirror  23  and the optical axis AX. 
     The lens member  12  is a prismatic member that functions as a lens as described above and refracts and also transmits the imaging light GL from the first mirror  21 . The lens member  12  includes a refractive portion (incident portion)  12   a  disposed on an incident side and a refractive portion (emitting portion)  12   b  disposed on an emission side. The refractive portions  12   a  and  12   b  are each a free curved surface, for example. The lens member  12  may be formed of, for example, a resin, but may also be formed of glass. 
     The first mirror  21  is a plate-like component that functions as a concave front surface mirror and reflects the imaging light GL passing through the lens member  12  from the display device  11 . Regarding the structure of the first mirror  21 , specifically, the first mirror  21  is a mirror plate  21   a  having a structure in which a reflection film  21   c  is provided on a front surface  21   s  of a plate-like body  21   b . The reflecting portion  21   r  of the first mirror  21  is, for example, a free curved surface and has a shape corresponding to a front surface of the reflection film  21   c  or the front surface  21   s  of the plate-like body  21   b . The reflecting portion  21   r  is not limited to a free curved surface and may be an aspheric surface. The reflecting portion  21   r  is asymmetric across the optical axis AX with respect to a first direction D 1  corresponding to the eccentric direction in the YZ plane and is symmetric across the optical axis AX with respect to a second direction D 2  or the X direction orthogonal to the first direction D 1 . The plate-like body  21   b  of the first mirror  21  is made of, for example, resin, but may also be made of glass. The reflection film  21   c  is formed of a single layer film or a multilayer film of metal such as Al and Ag, for example, but may also be a dielectric multilayer film. The reflection film  21   c  may be formed by lamination including a technique such as vapor deposition, but may also be formed by bonding a sheet-shaped reflective film. 
     In the first mirror  21  described above, an aberration reduction can be achieved by setting the reflecting portion  21   r  to be a free curved surface or an aspheric surface, and, particularly when a free curved surface is used, an aberration of the projection optical system  30 , which is a non-coaxial optical system or an eccentric optical system, can be easily reduced. The free curved surface is a surface without an axis of rotational symmetry, and various polynomials may be used as a surface function of the free curved surface. In addition, the aspheric surface is a surface having an axis of rotational symmetry, but is a paraboloid or a surface other than a spherical surface expressed by a polynomial. 
     The refractive reflective optical member  22  is a prismatic member that functions as a lens and a mirror and refracts and also reflects the imaging light GL from the first mirror  21 . The refractive reflective optical member  22  includes the refractive member  22   b  including a refractive portion  22   e  and a reflection film  22   c  provided at a non-refractive portion  22   d  of the refractive member  22   b . The refractive member  22   b  of the refractive reflective optical member  22  is made of, for example, resin, but may also be made of glass. The refractive member  22   b  may be formed of a material having an Abbe number of greater than or equal to 50 in terms of suppressing occurrence of chromatic aberrations. The reflection film  22   c  is formed of a single layer film or a multilayer film of metal such as Al and Ag, for example, but may also be a dielectric multilayer film. The reflection film  22   c  may be formed by laminating, and may also be formed by affixing a sheet-shaped reflection film. 
     The refractive portion  22   e  of the refractive reflective optical member  22  is, for example, a free curved surface, but may also be an aspheric surface. The refractive portion  22   e  is a common incidence-emission surface through which the imaging light GL passes before and after reflection by the mirror portion  22   r . In other words, a light beam from the first mirror  21  is refracted by the refractive portion  22   e  and incident into the refractive reflective optical member  22 , and, when being reflected by the mirror portion  22   r  and emitted to the outside of the refractive reflective optical member  22 , the light beam is refracted again by the refractive portion  22   e . The refractive portion  22   e  is asymmetric across the optical axis AX with respect to a first direction D 21  corresponding to the eccentric direction in the YZ plane, and is symmetric across the optical axis AX with respect to a second direction D 22  or the X direction orthogonal to the first direction D 21 . In the refractive reflective optical member  22 , the refractive portion  22   e  may be provided with an anti-reflective film. 
     The mirror portion  22   r  of the refractive reflective optical member  22  is, for example, a free curved surface and has a shape corresponding to an inner surface of the reflection film  22   c  or the non-refractive portion  22   d  of the refractive member  22   b . The mirror portion  22   r  is not limited to a free curved surface and may be an aspheric surface. The mirror portion  22   r  is asymmetric across the optical axis AX with respect to a first direction D 31  corresponding to the eccentric direction in the YZ plane and is symmetric across the optical axis AX with respect to a second direction D 32  or the X direction orthogonal to the first direction D 31 . 
     The second mirror  23  is a plate-like component that functions as a concave front surface mirror and reflects the imaging light GL from the refractive reflective optical member  22 . The second mirror  23  covers a position of the exit pupil EP in which the pupil EY is located and also has a concave shape toward the position of the exit pupil EP. The second mirror  23  is a mirror plate  23   a  having a structure in which a reflection film  23   c  is formed on a front surface  23   s  of a plate-like body  23   b . The reflecting portion  23   r  of the second mirror  23  is, for example, a free curved surface and has a shape corresponding to a front surface of the reflection film  23   c  or the front surface  23   s  of the plate-like body  23   b . The reflecting portion  23   r  is not limited to a free curved surface and may be an aspheric surface. The reflecting portion  23   r  is asymmetric across the optical axis AX with respect to a first direction D 41  corresponding to the eccentric direction in the YZ plane and is symmetric across the optical axis AX with respect to a second direction D 42  or the X direction orthogonal to the first direction D 41 . 
     The second mirror  23  is a transmissive type reflection element that transmits a portion of the imaging light GL upon reflection, and the reflection film  23   c  of the second mirror  23  has semi-transmissive properties. Accordingly, external light OL passes through the second mirror  23 , and thus a see-through view of externals is enabled, and a virtual image can be superimposed on an external image. At this time, when the plate-shaped body  23   b  has a thickness of less than or equal to approximately a few millimeters, a change in magnification of the external image can be curbed to be small. A reflectance of the reflection film  23   c  with respect to the imaging light GL and the external light OL is set to 10% or greater and 50% or less in a range of an incident angle of the assumed imaging light GL from the viewpoint of ensuring a brightness of the imaging light GL and facilitating observation of the external image by see-through. The plate-like body  23   b  of the second mirror  23  is made of, for example, resin, but may also be made of glass. The reflection film  23   c  is formed of, for example, a dielectric multilayer film configured of a plurality of dielectric layers having a film thickness adjusted. The reflection film  23   c  may also be a single layer film or a multilayer film of metal such as Al and Ag having a film thickness adjusted. The reflection film  23   c  may be formed by laminating, and may also be formed by affixing a sheet-shaped reflection film. 
     A distance between the positions of the second mirror  23  and the exit pupil EP is set to a certain interval (approximately 14 mm) along the optical axis AX on the emission side or the Z axis, ensuring that there is space for placing eyeglasses. The second mirror  23  can be provided with an anti-reflective film on the plate-like body  23   b  on the opposite side to where the reflection film  23   c  is provided. In other words, an anti-reflective film can be provided on the external side of the second mirror  23 . 
     As described above, an aberration reduction can be achieved by setting the refractive portion  12   a  and the refractive portion  12   b  of the lens member  12 , the reflecting portion  21   a  of the first mirror  21 , the refractive portion  22   e  of the refractive reflective optical member  22 , the mirror portion  22   r  of the refractive reflective optical member  22 , and the reflecting portion  23   r  of the second mirror  23  to be a free curved surface or an aspheric surface, and, particularly when a free curved surface is used, an aberration of the projection optical system  30  being a non-coaxial optical system or an eccentric optical system can be easily reduced. 
     In particular, in the present embodiment, the distance from the display unit  11   a  of the display device  11  to the reflecting portion  21   r  of the first mirror  21  is set to be shorter than the distance from the position of the exit pupil EP to the reflecting portion  23   r  of the second mirror  23 , and a first angle θ formed by the imaging light GL incident on the reflecting portion  23   r  of the second mirror  23  and the imaging light GL reflected by the reflecting portion  23   r  of the second mirror  23  is set to greater than 0° and 45° or less. Thus, circuit correction prompted by the occurrence of a distortion such as trapezoidal distortion can be made unnecessary or the amount needed can greatly reduced. Note that, here, the angle formed by the imaging light GL incident on the second mirror  23  and the imaging light GL reflected by the second mirror  23  represents the angle forming by the imaging light GL that travels along the optical axis AX and is incident and reflected at the second mirror  23 . 
     The optical path of the imaging light GL will be described below. First, the imaging light GL from the display device  11  passes through the lens member  12 , is incident on the first mirror  21 , and is reflected at a high reflectance close to 100% by the reflecting portion  21   r . The imaging light GL reflected by the first mirror  21  is incident on the refractive reflective optical member  22 , refracted by the refractive portion  22   e , reflected at a high reflectance close to 100% by the mirror portion  22   r , and refracted again by the refractive portion  22   e . The imaging light GL from the refractive reflective optical member  22  is incident on the second mirror  23  and reflected at a reflectance of less than or equal to approximately 50% by the reflecting portion  23   r . The imaging light GL reflected by the second mirror  23  is incident on the exit pupil EP where the pupil EY of the user US is. An intermediate image of the imaging light GL is formed between the refractive reflective optical member  22  and the second mirror  23 . The intermediate image is formed by appropriately enlarging an image formed on the display unit  11   a  of the display device  11 . The intermediate image does not intersect the refractive portion  22   e  to avoid the effects of unwanted matter and the like adhered to the refractive portion  22   e . An angle of view observed in the position of the exit pupil EP is assumed to be about 50° diagonally, for example. 
     The first mirror  21  and the second mirror  23  described above are not limited to front surface mirrors and may be rear surface mirrors with the plate-like body  21   b  including the reflection film  21   c  on a rear surface and the plate-like body  23   b  including the reflection film  23   c  on a rear surface. 
     As described above, instead of the refractive reflective optical member  22 , the first mirror  21  may be used as a refractive reflective optical member or the first mirror  21  and the refractive reflective optical member  22  may both be used as a refractive reflective optical member. 
     Referring now to  FIG.  4    and the like, the shape of the second mirror  23 , in particular, of the projection optical system  30  constituting the virtual image display apparatus  100  will be described. Note that  FIG.  4    is a perspective view illustrating an optical structure and the like of the virtual image display apparatus  100 ,  FIG.  5    is a side cross-sectional view for describing the shape of the second mirror  23  of the virtual image display apparatus  100 , and  FIG.  6    is a plane cross-sectional view of the same. 
     As illustrated in  FIG.  4    and as described above, the second mirror  23  has a concave shape toward the position of the exit pupil EP. Accordingly, regarding the area of the second mirror  23  on a curved line in the up-and-down direction (±Y direction), an area  23   o  on the curved line traveling along the center of the second mirror  23  and an area  23   p  traveling along an end side of the second mirror  23  are difference in terms of distance. 
     For example, in  FIG.  5   , an imaging light GLo indicated by a dashed line is an imaging light reflected at or near the area  23   o  of the second mirror  23  toward the exit pupil EP. Also, an imaging light GLp indicated by a solid line is an imaging light reflected at or near the area  23   p  of the second mirror  23  toward the exit pupil EP. Note that the imaging light GLo and the imaging light GLp emitted from the same position (same height) in the ±Y direction from the display device  11  overlap in  FIG.  5   . However, as illustrated in  FIG.  6   , when viewed from above (+Y side), the imaging light GLo and the imaging light GLp emitted from the same height from the display device  11  do not overlap. That is, regarding the imaging light GLo and the imaging light GLp emitted from different positions in the X direction, as indicated by the arrows in  FIG.  6    for example, the imaging light GLo is reflected at or near the area  23   o  of the second mirror  23  and the imaging light GLp is reflected at or near the area  23   p  of the second mirror  23 . Returning to  FIG.  5   , even when the imaging light GLo and the imaging light GLp are emitted from the same height in the ±Y direction from the display device  11 , a distance difference DD between reflection positions at the second mirror  23  is a difference of approximately 4 mm. In the example in  FIG.  5   , a distance difference DD 1  between imaging light emitted from the height of a center position (reference position) of the display device  11 , in other words, the imaging light GLo emitted along the optical axis AX and the imaging light GLp emitted from a peripheral side of the optical axis AX, is 4.0 mm. Also, a distance difference DD 2  between the imaging light GLo and the imaging light GLp emitted from the display device  11  at a height (upper end) 3 mm separated in the upward direction (+Y direction) from the center position (reference position) is 4.2 mm. Also, a distance difference DD 3  between the imaging light GLo and the imaging light GLp emitted from the display device  11  at a position (lower end) 3 mm separated in the downward direction (−Y direction) from the center position (reference position) is 3.5 mm. The second mirror  23  is curved in a manner to produce a difference as described above. 
     Next, an example of an arrangement relationship of the members constituting the optical system of the virtual image display apparatus  100  and a comparision method thereof will be described with reference to  FIG.  7    and the like. Note that  FIG.  8    is a conceptual diagram illustrating the arrangement of the members extracted from  FIG.  7    illustrating the arrangement relationship of the members. 
     First, as illustrated in  FIG.  7   , herein, the arrangement relationship (positional relationship) of the members is defined using a position of each member where the optical axis AX passes through as the reference position. For example, in the case of the position of the exit pupil EP, a point EPx indicting a center position, which is the position where the optical axis AX meets the exit pupil EP, is the reference position. In a similar manner, the reference position of the second mirror  23  is a point  23   x , the reference position of the refractive reflective optical member  22  (the mirror portion  22   r ) is a point  22   x , the reference position of the first mirror  21  (reflecting portion  21   r ) is a point  21   x , and the reference position of the display device  11  (display unit  11   a ) is a point  11   x.    
     Also, the X direction, the Y direction, and the Z direction are used for directions. In this case, regarding the the X direction, the Y direction, and the Z direction, under the assumption that the virtual image display apparatus  100  is mounted in an ideal (virtual) state design-wise, the Z direction corresponds to forward or front direction from the perspective of the virtual user US, the X direction corresponds to the lateral direction (horizontal direction) in which both eyes are aligned, and the Y direction corresponds to the vertical direction. 
     Accordingly, as illustrated in  FIG.  7    for example, the distance LL 1  is shorter than the distance LL 2 , where, in the Z direction, the distance from the display device  11  to the first mirror  21  is defined as a distance LL 1  and the distance from the position of the exit pupil EP to the second mirror  23  is defined as a distance LL 2 . It follows that the distance from the display device  11  to the first mirror  21  can be understood to be shorter than the distance from the position of the exit pupil EP to the second mirror  23 . 
     Also, in the virtual image display apparatus  100 , in an ideal state as described above, the direction of the optical axis AX from the second mirror  23  to the exit pupil EP is inclined slightly diagonally downward with respect to the Z direction as illustrated in  FIGS.  7  and  8   . From a perspective of ergonomics, a natural human line-of-sight angle is known to be approximately 10° downward, and also when visually perceiving an image (virtual image) from the virtual image display apparatus  100 , shifting the center of the image 10° downward with respect to a reference corresponding to the Z direction may conceivably allow for a more nature and pleasant image viewing experience. Thus, in an ideal state as illustrated in the diagrams, the direction of the optical axis AX from the second mirror  23  to the exit pupil EP is configured to have a 10° downward incline in the up-and-down direction. In other words, in the diagrams, α=10°, where α is an inclination angle (line-of-sight inclination with respect to the Y direction) with respect to the Z direction of the optical axis AX toward the exit pupil EP. 
     Also, as illustrated in the diagrams, regarding the point EPx indicating the reference position of the exit pupil EP and the point  22   x  indicating the reference position of the refractive reflective optical member  22 , of the distance from the point EPx to the point  22   x , the distance in the Y direction (vertical direction) is defined as distance y and the distance in the Z direction (front-and-back direction) is defined as distance z. 
     Also, in this case, as described above, the angle formed by the imaging light GL incident on the second mirror  23  and the imaging light GL reflected by the second mirror  23  is treated as an angle representing the angle of the imaging light GL along the optical axis AX and is defined as the first angle θ. By increasing the first angle θ, it is expected that the portion of the virtual image display apparatus  100  overall positioned in front of the eyes can be kept from protruding out too far. However, when the degree of eccentricity with respect to the light guiding direction (−Y direction) of the imaging light GL increases, the occurring aberration also increases. In the case of the above-described mode, in particular, it is considered that the effects on light guiding in the vertical direction (Y direction) are greater and distortion aberration caused by a bias in the corresponding direction, in other words the vertical direction of the image, occurs more easily. Thus, from a perspective of aberration suppression, it is necessary to make the first angle θ small to some extent. 
     Furthermore, here, the distance along the optical axis AX from the position of the exit pupil EP (the point EPx) to the second mirror  23  (the point  23   x ) is defined as a distance C. That is, the distance C indicates the position of the second mirror  23  relative to the position of the eye of the user US, which is one of the indicators indicating the size in the front of the eyes relative to the virtual image display apparatus  100  overall. 
     Here, as can be seen from  FIG.  8   , the parameters, in other words the angle a, the distance y, the distance z, the distance C, and the first angle θ described above, of the optical axis AX from the point  22   x  indicating the reference position of the refractive reflective optical member  22  (the mirror portion  22   r ) to the point EPx are geometrically extracted and a relationship expressed by Formula (1) below is established. 
     
       
         
           
             
               
                 
                   C 
                   = 
                   
                     
                       y 
                       + 
                       
                         z 
                         * 
                         tan 
                         ⁢ 
                            
                         
                           ( 
                           
                             θ 
                             + 
                             α 
                           
                           ) 
                         
                       
                     
                     
                       
                         cos 
                         ⁢ 
                            
                         
                           ( 
                           α 
                           ) 
                         
                         * 
                         tan 
                         ⁢ 
                            
                         
                           ( 
                           
                             θ 
                             + 
                             α 
                           
                           ) 
                         
                       
                       - 
                       
                         sin 
                         ⁢ 
                            
                         
                           ( 
                           α 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     C: The distance from the position of the exit pupil EP to the second mirror  23   
     y: The distance in the Y direction (vertical direction) from the position of the exit pupil EP to the position of the refractive reflective optical member  22   
     z: The distance in the Z direction (horizontal direction) from the position of the exit pupil EP to the position of the refractive reflective optical member  22   
     α: The inclination angle of the line-of-sight of the user US with respect to the Z direction (horizontal direction) 
     θ: The first angle formed by the imaging light GL incident on the second mirror  23  and the imaging light GL reflected by the second mirror  23   
     Here, the exit pupil EP is located at an eye position for the user US, the refractive reflective optical member  22  is located at a position closest to the forehead of the user US in the optical system. Thus, of those described above, the distance y and the distance z indicating the relative positional relationship between the exit pupil EP and the refractive reflective optical member  22  have numerical values in a relatively determined range, with typical examples expected to be y=14.5 mm and z=18.4 mm. 
     Also, of those described above, the inclination angle a of the line-of-sight is expected to be, in a typical example, α=10°. 
     From those above, when the distance y, the distance z, and the angle a are specified values, the Formula (1) described above indicates a relationship that should be satisfied by the first angle θ and the distance C from the position of the exit pupil EP and the second mirror  23 . In this case, taking into consideration  FIG.  8    and also the Formula (1) described above, the greater the distance C is, the smaller the first angle θ can be, and this allows the occurrence of aberrations in the optical system to be suppressed. However, the distance C indicates the position of the second mirror  23  with respect to the position of the eye of the user US, and thus the greater the distance C is, the more the overall size of the apparatus is increased. 
     In the present embodiment, by the first angle θ being greater than 0° and 45° or less, a configuration that suppresses aberration is achieved and, taking into consideration of the Formula (1) described above, the range of the distance C is kept to an appropriate range. This allows increases to the size of the apparatus to be suppressed. 
     Note that the value of the distance C is less than 100 mm, for example, and more preferably approximately from 70 mm to 80 mm or less from the perspective of the overall size of the apparatus and ensuring an angle that will ensure the reflecting region of the second mirror  23 . Accordingly, it is expected that the lower limit value of the first angle θ is, for example, approximately 10°. 
     Referring back to  FIG.  7   , here in addition to those described above, an angle formed by the imaging light GL incident on the first mirror  21  and the imaging light GL reflected by the first mirror  21  is also defined as a second angle φ. The second angle φ, following from specify the first angle θ, is considered to be an angle representative of the second angle φ and is, for example, an angle of the components of the imaging light GL along the optical axis AX before and after the first mirror  21 . Note that in the illustrated example, the first angle θ is smaller than the second angle φ. 
       FIG.  9    is a conceptual diagram illustrating a state of an occurring aberration (distortion aberration). In the diagram, grid-like lines DA 1  indicated by dashed lines correspond to the shape of a display image DA formed on the display unit  11   a  of the display device  11 . In this case, the grid-like lines DA 1  form a rectangular shape. On the other hand, grid-like lines IG indicated by solid lines indicate the shape of an image visually perceivably as a virtual image. In the diagram, the shapes are enlarged or reduced and superimposed to allow the shapes to be compared. In this case, it can be seen that there is some distortion but the shape basically retains a rectangular-shape, in other words there is basically no distortion aberration, and distortion in the vertical and horizontal directions in the optical system is removed. Here, for example, when a see-through image such as one formed by the virtual image display apparatus  100  is visually perceived, good visibility is considered to be maintained if the distortion is 5% or less and preferably from 2 to 3% compared to the original image without distortion. In the present embodiment, by setting the first angle θ to be greater than 0° and 45° or less, distortion occurring in the eccentric optical system can be sufficiently suppressed in the optical system, allowing for good image formation to be performed without requiring circuit correction or with keeping an increase in the burden due to circuit correction to a minimum. 
     Note that  FIG.  10    is a graph (MTF diagram) illustrating the resolution of the mode described above. It can be seen from  FIG.  10    that image formation is formed in a sufficiently good state. 
     As described above, the virtual image display apparatus  100  includes the display device  11 , which is an imaging light emitting unit configured to emit the imaging light GL; the first mirror  21  configured to reflect the imaging light GL from the display device  11 ; the refractive reflective optical member  22 , which is an optical member including a the mirror portion  22   r  configured to reflect the imaging light GL reflected by the first mirror  21 ; and the second mirror  23  configured to reflect the imaging light GL reflected by the mirror portion  22   r  toward the position of the exit pupil EP, wherein the distance (the distance LL 1 ) from the display device  11  to the first mirror  21  is shorter than the distance (the distance LL 2 ) from the position of the exit pupil EP to the second mirror  23 ; and the first angle θ formed by the imaging light GL incident on the second mirror  23  and the imaging light GL reflected by the second mirror  23  is greater than 0° and 45° or less. In the virtual image display apparatus  100 , the distance C from the position of the exit pupil EP to the position of the second mirror  23  is provided and the first angle θ formed by the imaging light GL incident on the second mirror  23  and the imaging light GL reflected by the second mirror  23  is greater than 0° and 45° or less. This allows the occurrence of distortion to be sufficiently suppressed, and allows for image formation with high accuracy to be performed without requiring electrical correction and the like by a correction circuit, for example. 
     Example 1 
     Hereinafter, Example 1, which is an implementation of the optical system of the virtual image display apparatus  100  according to the first embodiment, will now be described. 
     Table 1 below lists parameters for each surface constituting the virtual image display apparatus of Example 1. The unit of distance in the table is mm. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 SURFACE 
                   
                 SURFACE 
                 CURVATURE 
                   
                 REFRACTION/ 
               
               
                 NUMBER 
                 SURFACE NAME 
                 TYPE 
                 RADIUS 
                 MATERIAL 
                 REFLECTION 
               
               
                   
               
               
                 1 
                 EXIT PUPIL EP 
                 SPHERE 
                 INFINITE 
                 — 
                 REFRACTION 
               
               
                 2 
                 SECOND MIRROR 23 
                 XY 
                 −4.106 
                   
                 REFLECTION 
               
               
                   
                   
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 3 
                 INCIDENCE- 
                 XY 
                 −14.12 
                 RESIN A 
                 REFRACTION 
               
               
                   
                 EMISSION PORTION 
                 POLYNOMIAL 
               
               
                   
                 22e OF REFRACTIVE 
                 SURFACE 
               
               
                   
                 REFLECTIVE 
               
               
                   
                 OPTICAL MEMBER 22 
               
               
                 4 
                 the mirror 
                 XY 
                 −97.56 
                 RESIN A 
                 REFLECTION 
               
               
                   
                 portion 22r OF 
                 POLYNOMIAL 
               
               
                   
                 REFRACTIVE 
                 SURFACE 
               
               
                   
                 REFLECTIVE 
               
               
                   
                 OPTICAL MEMBER 22 
               
               
                 5 
                 INCIDENCE- 
                 XY 
                 −14.12 
                   
                 REFRACTION 
               
               
                   
                 EMISSION PORTION 
                 POLYNOMIAL 
               
               
                   
                 22e OF REFRACTIVE 
                 SURFACE 
               
               
                   
                 REFLECTIVE 
               
               
                   
                 OPTICAL MEMBER 22 
               
               
                 6 
                 FIRST MIRROR 21 
                 XY 
                 −22.01 
                   
                 REFLECTION 
               
               
                   
                   
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 7 
                 REFRACTIVE 
                 XY 
                 −12.184 
                 RESIN B 
                 REFRACTION 
               
               
                   
                 PORTION 12b 
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 8 
                 REFRACTIVE 
                 XY 
                 −10.678 
                   
                 REFRACTION 
               
               
                   
                 PORTION 12a 
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 9 
                 COVER GLASS 
                 SPHERE 
                 INFINITE 
                 SILICA 
                 REFRACTION 
               
               
                 10 
                 DISPLAY UNIT 11a 
                 SPHERE 
                 INFINITE 
                   
                 REFRACTION 
               
               
                   
               
            
           
           
               
               
               
            
               
                 SURFACE 
                 GLOBAL COORDINATES 
                   
               
            
           
           
               
               
               
               
               
            
               
                 NUMBER 
                 x 
                 y 
                 z 
                 α 
               
               
                   
               
               
                 1 
               
               
                 2 
                 0 
                 7.58 
                 48.72 
                 13.7 
               
               
                 3 
                 0 
                 12.34 
                 21.93 
                 16.5 
               
               
                 4 
                 0 
                 14.54 
                 18.52 
                 22.8 
               
               
                 5 
                 0 
                 15.23 
                 22.62 
                 18.5 
               
               
                 6 
                 0 
                 21.04 
                 33.58 
                 20 
               
               
                 7 
                 0 
                 23 
                 22.07 
                 17.5 
               
               
                 8 
                 0 
                 23.51 
                 19.33 
                 2.52 
               
               
                 9 
                 0 
                 23.59 
                 18.86 
                 0 
               
               
                 10 
                 0 
                 23.69 
                 17.88 
                 0 
               
               
                   
               
            
           
         
       
     
     In this case, a light beam is followed from the exit pupil EP toward the display unit  11   a . In table 1, the surface interval between adjacent surfaces, the material for the refractive medium, the surface distinction that is the refraction or reflection, and the global coordinates of each surface are described. Note that, for the material for the refractive medium, the resin A means a resin material having a refractive index of approximately 1.52 in a visible range and an Abbe number of 56.5, the resin B means a resin material having a refractive index of approximately 1.67 in a visible range and an Abbe number of 19.2, and SILICA means a quartz glass having a refractive index of approximately 1.47 in the visible range. 
     The data of Example 1 listed in Table 1 above shows that the free curved surface is represented by an xy polynomial surface, and the coefficient of the xy polynomial surface is given by the following Formula using z as the optical axis direction. 
     
       
         
           
             
               
                 
                   z 
                   = 
                   
                     
                       
                         ε 
                         ⁢ 
                         
                           r 
                           2 
                         
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   k 
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 c 
                                 2 
                               
                               ⁢ 
                               
                                 r 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           2 
                         
                         66 
                       
                         
                       
                         
                           C 
                           j 
                         
                         ⁢ 
                         
                           x 
                           m 
                         
                         ⁢ 
                         
                           y 
                           n 
                         
                       
                     
                   
                 
               
               
                 
                   j 
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               m 
                               + 
                               n 
                             
                             ) 
                           
                           2 
                         
                         + 
                         m 
                         + 
                         
                           3 
                           ⁢ 
                           n 
                         
                       
                       2 
                     
                     + 
                     1 
                   
                 
               
             
           
         
       
     
     z: Sag amount of surface parallel with z axis 
     c: Vertex curvature 
     k: Conic coefficient 
     C j : Coefficient of monomial x m y n    
     r: Distance in radius direction (r=√(x 2 +y 2 )) 
     Note that C i =C j ×{(normalized radius) (m+n− 1)}. 
     Table 2 below is a table listing specific examples of the coefficient C i . 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 Ci 
                   
                   
               
               
                   
                 C1 
                 k 
                 CONIC CONSTANT 
               
               
                   
                 C2 
                 x 
                 COEFFICIENT OF 
               
               
                   
                 C3 
                 y 
                 COEFFICIENT OF 
               
               
                   
                 C4 
                 x2 
                 COEFFICIENT OF 
               
               
                   
                 C5 
                 xy 
                 COEFFICIENT OF 
               
               
                   
                 C6 
                 y2 
                 COEFFICIENT OF 
               
               
                   
                 C7 
                 x3 
                 COEFFICIENT OF 
               
               
                   
                 C8 
                 x2y 
                 COEFFICIENT OF 
               
               
                   
                 C9 
                 xy2 
                 COEFFICIENT OF 
               
               
                   
                 C10 
                 y3 
                 COEFFICIENT OF 
               
               
                   
                 C11 
                 x4 
                 COEFFICIENT OF 
               
               
                   
                 C12 
                 x3y 
                 COEFFICIENT OF 
               
               
                   
                 C13 
                 x2y2 
                 COEFFICIENT OF 
               
               
                   
                 C14 
                 xy3 
                 COEFFICIENT OF 
               
               
                   
                 C15 
                 y4 
                 COEFFICIENT OF 
               
               
                   
                 C16 
                 x5 
                 COEFFICIENT OF 
               
               
                   
                 C17 
                 x4y 
                 COEFFICIENT OF 
               
               
                   
                 C18 
                 x3y2 
                 COEFFICIENT OF 
               
               
                   
                 C19 
                 x2y3 
                 COEFFICIENT OF 
               
               
                   
                 C20 
                 xy4 
                 COEFFICIENT OF 
               
               
                   
                 C21 
                 y5 
                 COEFFICIENT OF 
               
               
                   
                 C22 
                 x6 
                 COEFFICIENT OF 
               
               
                   
                 C23 
                 x5y 
                 COEFFICIENT OF 
               
               
                   
                 C24 
                 x4y2 
                 COEFFICIENT OF 
               
               
                   
                 C25 
                 x3y3 
                 COEFFICIENT OF 
               
               
                   
                 C26 
                 x2y4 
                 COEFFICIENT OF 
               
               
                   
                 C27 
                 xy5 
                 COEFFICIENT OF 
               
               
                   
                 C28 
                 y6 
                 COEFFICIENT OF 
               
               
                   
                 C29 
                 x7 
                 COEFFICIENT OF 
               
               
                   
                 C30 
                 x6y 
                 COEFFICIENT OF 
               
               
                   
                 C31 
                 x5y2 
                 COEFFICIENT OF 
               
               
                   
                 C32 
                 x4y3 
                 COEFFICIENT OF 
               
               
                   
                 C33 
                 x3y4 
                 COEFFICIENT OF 
               
               
                   
                 C34 
                 x2y5 
                 COEFFICIENT OF 
               
               
                   
                 C35 
                 xy6 
                 COEFFICIENT OF 
               
               
                   
                 C36 
                 y7 
                 COEFFICIENT OF 
               
               
                   
                 C37 
                 x8 
                 COEFFICIENT OF 
               
               
                   
                 C38 
                 x7y 
                 COEFFICIENT OF 
               
               
                   
                 C39 
                 x6y2 
                 COEFFICIENT OF 
               
               
                   
                 C40 
                 x5y3 
                 COEFFICIENT OF 
               
               
                   
                 C41 
                 x4y4 
                 COEFFICIENT OF 
               
               
                   
                 C42 
                 x3y5 
                 COEFFICIENT OF 
               
               
                   
                 C43 
                 x2y6 
                 COEFFICIENT OF 
               
               
                   
                 C44 
                 xy7 
                 COEFFICIENT OF 
               
               
                   
                 C45 
                 y8 
                 COEFFICIENT OF 
               
               
                   
                   
               
            
           
         
       
     
     Table 3 below is a table providing a summary of the polynomial coefficients Ci that give a free curved surface included in Example 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 SURFACE NUMBER 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 NORMALIZED 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
               
               
                 RADIUS 
               
               
                 C1 
                 −1 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C2 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C3 
                 −9.0291 
                 0.3350 
                 −80.4496 
                 0.3350 
                 3.8993 
                 2.5791 
                 6.8181 
               
               
                 C4 
                 9.8402 
                 −1.1805 
                 −22.8106 
                 −1.1806 
                 2.6543 
                 −0.3600 
                 0.5367 
               
               
                 C5 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C6 
                 9.5401 
                 −1.2298 
                 27.5978 
                 −1.2296 
                 3.7110 
                 4.9874 
                 10.8911 
               
               
                 C7 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C8 
                 0.0156 
                 0.1271 
                 −76.4135 
                 0.1271 
                 2.9937 
                 −25.2712 
                 −39.8347 
               
               
                 C9 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C10 
                 1.8219 
                 0.6180 
                 91.7462 
                 0.6180 
                 1.4769 
                 −5.3634 
                 −8.2641 
               
               
                 C11 
                 −1.6142 
                 0.3100 
                 9.0212 
                 0.3100 
                 −4.5835 
                 −5.9867 
                 −17.9952 
               
               
                 C12 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C13 
                 0.2187 
                 −0.5168 
                 −199.1072 
                 −0.5168 
                 0.3421 
                 −42.3371 
                 −86.3267 
               
               
                 C14 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C15 
                 −0.1083 
                 1.1462 
                 −97.0445 
                 1.1462 
                 −0.1056 
                 −3.6247 
                 −25.1239 
               
               
                 C16 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C17 
                 2.4123 
                 1.9471 
                 60.7310 
                 1.9471 
                 −4.7776 
                 −8.8809 
                 −28.7075 
               
               
                 C18 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C19 
                 0.3817 
                 1.4052 
                 −494.7267 
                 1.4052 
                 −0.0834 
                 −21.9315 
                 −36.2182 
               
               
                 C20 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C21 
                 −0.0347 
                 1.7105 
                 −343.5757 
                 1.7105 
                 −0.1521 
                 −0.0598 
                 −18.8767 
               
               
                 C22 
                 −0.0709 
                 0 
                 23.0613 
                 0 
                 2.2831 
                 0 
                 0 
               
               
                 C23 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C24 
                 −1.2313 
                 0 
                 118.9659 
                 0 
                 1.0305 
                 0 
                 0 
               
               
                 C25 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C26 
                 −0.2629 
                 0 
                 −777.6150 
                 0 
                 0.0443 
                 0 
                 0 
               
               
                 C27 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C28 
                 −0.0170 
                 0 
                 −285.4844 
                 0 
                 −0.0337 
                 0 
                 0 
               
               
                 C29 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C30 
                 0.0425 
                 0 
                 58.3577 
                 0 
                 3.0839 
                 0 
                 0 
               
               
                 C31 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C32 
                 0.2625 
                 0 
                 89.4878 
                 0 
                 2.2992 
                 0 
                 0 
               
               
                 C33 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C34 
                 0.0567 
                 0 
                 −601.9941 
                 0 
                 −0.1774 
                 0 
                 0 
               
               
                 C35 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C36 
                 0.0067 
                 0 
                 −39.4808 
                 0 
                 −0.0320 
                 0 
                 0 
               
               
                 C37 
                 −0.0003 
                 0 
                 −0.2500 
                 0 
                 0.0082 
                 0 
                 0 
               
               
                 C38 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C39 
                 −0.0062 
                 0 
                 37.9565 
                 0 
                 1.0280 
                 0 
                 0 
               
               
                 C40 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C41 
                 −0.0202 
                 0 
                 20.5279 
                 0 
                 0.5523 
                 0 
                 0 
               
               
                 C42 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C43 
                 −0.0042 
                 0 
                 −175.5070 
                 0 
                 −0.0897 
                 0 
                 0 
               
               
                 C44 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C45 
                 −0.0006 
                 0 
                 20.0994 
                 0 
                 −0.0105 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
     Second Embodiment 
     Next, a virtual image display apparatus according to the second embodiment of the present disclosure will be described with reference to  FIG.  11    and the like. Note that the virtual image display apparatus according the second embodiment is obtained by modifying a part of the virtual image display apparatus according to the first embodiment, and description of common portions will be omitted. Note that  FIG.  11    is a diagram corresponding to  FIG.  3   , and  FIG.  12    is a diagram corresponding to  FIG.  9   . 
     As illustrated in  FIG.  11   , the virtual image display apparatus  100  of the second embodiment includes, as the projection optical system  30 , the lens member  12 , the first mirror  21 , the refractive reflective optical member  22 , and the second mirror  23  in a similar manner to the first embodiment and further includes a correction circuit CC in the display device  11 . In the present embodiment, the occurrence of vertical distortion (distortion in the vertical direction of the image) is suppressed in the optical system and horizontal distortion (distortion in the horizontal direction of the image) is subjected to circuit correction by the correction circuit CC, making this mode different from the first embodiment, which suppressed aberrations including both vertical distortion and horizontal distortion. Note that as illustrated in the diagram, in the present embodiment also, the distance from the display device  11  to the first mirror  21  is shorter than the distance from the position of the exit pupil EP to the second mirror  23 . 
       FIG.  12    is a conceptual diagram illustrating a state of an occurring aberration (distortion aberration) in the optical system when correction by the correction circuit CC is not performed, for example. In the diagram, in a similar manner to  FIG.  9   , the grid-like lines DA 1  indicated by dashed lines correspond to the shape of the display image DA formed on the display unit  11   a  of the display device  11 , and grid-like lines IGα indicated by solid lines indicated an image of when correction by the correction circuit CC is not performed. In other words, as is clear from the state illustrated in  FIG.  12   , in the case of the present embodiment, vertical distortion is removed from the optical system, but horizontal distortion remains. In this case, however, as can be seen from  FIG.  12   , when position adjustment of the pixels relating to the horizontal lines is performed by calculation processing in the correction circuit CC, an image with sufficient distortion correction can be formed. That is, the burden on the correction circuit CC can be reduced. In particular, in the present embodiment as described above, because aberrations including vertical distortion is suppressed due to the optical system being an eccentric optical system developed in the vertical direction, overall the occurrence of aberration can be effectively suppressed. 
     Example 2 
     Hereinafter, Example 2, which is an implementation of the optical system of the virtual image display apparatus  100  according to the second embodiment, will now be described. Data of Example 2 are also expressed in a manner similar to the data of Example 1, and redundant descriptions of the definitions and the like of the terms are omitted. 
     Table 4 below lists parameters for each surface constituting the virtual image display apparatus of Example 2. The unit of distance in the table is mm. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 SURFACE 
                   
                 SURFACE 
                 CURVATURE 
                   
                 REFRACTION/ 
               
               
                 NUMBER 
                 SURFACE NAME 
                 TYPE 
                 RADIUS 
                 MATERIAL 
                 REFLECTION 
               
               
                   
               
               
                 1 
                 EXIT PUPIL EP 
                 SPHERE 
                 INFINITE 
                   
                 REFRACTION 
               
               
                 2 
                 SECOND MIRROR 23 
                 XY 
                 −3.935 
                   
                 REFLECTION 
               
               
                   
                   
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 3 
                 INCIDENCE-EMISSION 
                 XY 
                 −12.310 
                 RESIN A 
                 REFRACTION 
               
               
                   
                 PORTION 22e OF 
                 POLYNOMIAL 
               
               
                   
                 REFRACTIVE 
                 SURFACE 
               
               
                   
                 REFLECTIVE OPTICAL 
               
               
                   
                 MEMBER 22 
               
               
                 4 
                 the mirror portion 
                 XY 
                 −15.650 
                 RESIN A 
                 REFLECTION 
               
               
                   
                 22r OF REFRACTIVE 
                 POLYNOMIAL 
               
               
                   
                 REFLECTIVE OPTICAL 
                 SURFACE 
               
               
                   
                 MEMBER 22 
               
               
                 5 
                 INCIDENCE-EMISSION 
                 XY 
                 −12.310 
                   
                 REFRACTION 
               
               
                   
                 PORTION 22e OF 
                 POLYNOMIAL 
               
               
                   
                 REFRACTIVE 
                 SURFACE 
               
               
                   
                 REFLECTIVE OPTICAL 
               
               
                   
                 MEMBER 22 
               
               
                 6 
                 FIRST MIRROR 21 
                 XY 
                 −19.000 
                   
                 REFLECTION 
               
               
                   
                   
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 7 
                 REFRACTIVE PORTION 
                 XY 
                 9.130 
                 RESIN B 
                 REFRACTION 
               
               
                   
                 12b 
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 8 
                 REFRACTIVE PORTION 
                 XY 
                 INFINITE 
                   
                 REFRACTION 
               
               
                   
                 12a 
                 POLYNOMIAL 
               
               
                   
                   
                 SURFACE 
               
               
                 9 
                 COVER GLASS 
                 SPHERE 
                 INFINITE 
                 SILICA 
                 REFRACTION 
               
               
                 10 
                 DISPLAY UNIT 11a 
                 SPHERE 
                 INFINITE 
                   
                 REFRACTION 
               
               
                   
               
            
           
           
               
               
               
            
               
                 SURFACE 
                 GLOBAL COORDINATES 
                   
               
            
           
           
               
               
               
               
               
            
               
                 NUMBER 
                 x 
                 y 
                 z 
                 α 
               
               
                   
               
               
                 1 
               
               
                 2 
                 0 
                 −7 
                 41.87 
                 17.6 
               
               
                 3 
                 0 
                 13 
                 21.6 
                 21.9 
               
               
                 4 
                 0 
                 16 
                 17.65 
                 30.3 
               
               
                 5 
                 0 
                 18 
                 22.36 
                 15.7 
               
               
                 6 
                 0 
                 24 
                 32.34 
                 21 
               
               
                 7 
                 0 
                 26 
                 21.88 
                 7.38 
               
               
                 8 
                 0 
                 26 
                 18.91 
                 7.64 
               
               
                 9 
                 0 
                 27 
                 18.12 
                 2.52 
               
               
                 10 
                 0 
                 27 
                 17.02 
                 1.73 
               
               
                   
               
            
           
         
       
     
     Table 5 below is a table providing a summary of the polynomial coefficients C i  that give a free curved surface included in Example 2. 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 SURFACE NUMBER 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 NORMALIZED 
                 10  
                 10  
                 10  
                 10  
                 10  
                 1 
                 1 
               
               
                 RADIUS 
               
               
                 C1 
                 −1  
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C2 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C3 
                 −7.529E+00  
                 −5.390E+00  
                 −6.387E+01  
                 −5.390E+00  
                 1.843E+00 
                 0.000E+00 
                 2.187E−01 
               
               
                 C4 
                 1.587E+01 
                 −6.394E−01  
                 −1.753E+01  
                 −6.394E−01  
                 3.989E+00 
                 −7.821E−02  
                 −1.008E−03  
               
               
                 C5 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C6 
                 8.741E+00 
                 −3.046E+00  
                 3.532E+01 
                 −3.048E+00  
                 2.517E+00 
                 −9.019E−02  
                 1.877E−02 
               
               
                 C7 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C8 
                 −9.621E+00  
                 −1.472E+00  
                 −8.325E+01  
                 −1.472E+00  
                 8.266E+00 
                 0.000E+00 
                 −3.842E−03  
               
               
                 C9 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C10 
                 2.166E+00 
                 −2.882E+00  
                 1.385E+02 
                 −2.882E+00  
                 1.833E+00 
                 0.000E+00 
                 −9.130E−03  
               
               
                 C11 
                 −8.574E−01  
                 1.649E−01 
                 −3.885E+01  
                 1.649E−01 
                 4.928E+00 
                 −4.620E−04  
                 −1.621E−04  
               
               
                 C12 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C13 
                 4.638E+00 
                 5.164E−01 
                 −3.097E+02  
                 5.164E−01 
                 1.921E+00 
                 −1.450E−03  
                 −1.008E04      
               
               
                 C14 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C15 
                 −4.939E−02  
                 −2.258E+00  
                 −1.626E+02  
                 −2.258E+00  
                 −2.228E−01  
                 2.559E−03 
                 2.058E−04 
               
               
                 C16 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C17 
                 2.171E+00 
                 −8.669E−01  
                 −6.175E+01  
                 −9.869E−01  
                 2.241E+01 
                 0.000E+00 
                 2.462E−05 
               
               
                 C18 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C19 
                 4.321E−01 
                 −1.136E+00  
                 −1.040E+03  
                 −1.136E+00  
                 −2.254E+00  
                 0.000E+00 
                 8.874E−05 
               
               
                 C20 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C21 
                 −3.497E−02  
                 −1.804E+00  
                 −6.961E+02  
                 −1.804E+00  
                 −5.449E−01  
                 0.000E+00 
                 1.913E−04 
               
               
                 C22 
                 −1.060E+00  
                 0.000E+00 
                 −5.279E+01  
                 0.000E+00 
                 2.020E+00 
                 3.836E−06 
                 2.176E−05 
               
               
                 C23 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C24 
                 −1.522E+00  
                 0.000E+00 
                 1.762E+02 
                 0.000E+00 
                 3.214E+01 
                 6.015E−05 
                 4.504E−08 
               
               
                 C25 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C26 
                 −8.398E−01  
                 0.000E+00 
                 −1.928E+03  
                 0.000E+00 
                 −2.809E+00  
                 3.885E−05 
                 −2.124E−05  
               
               
                 C27 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
                 0.000E+00 
               
               
                 C28 
                 −5.326E−02  
                 0.000E+00 
                 −5.302E+02  
                 0.000E+00 
                 −3.205E−02  
                 −1.376E−04  
                 1.370E−05 
               
               
                 C29 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C30 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C31 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C32 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C33 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C34 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C35 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C36 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C37 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C38 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C39 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C40 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C41 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C42 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C43 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C44 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C45 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
       FIG.  13    is a graph showing the relationship between the first angle θ (unit° on the vertical axis and the angle of view (unit°, diagonal angle of view) on the horizontal axis. In the diagram, a point PP0 indicates an example, as a comparative example, of a case where vertical and horizontal distortion remains present, in other words distortion correction has not been performed. In this case, the first angle θ is greater than 45° at an angle of view of 50° as seen from the position of the point PP0. In this case, though the possibility of decreasing the size of the apparatus can be considered, a large aberration would occur, requiring another method of correction via a circuit, panel shape, of the like. 
     In contrast, a point PP1 indicates an example of the first embodiment, in other words, a case where both vertical distortion and horizontal distortion have been corrected. In this case, the first angle θ is greater than 0° and 45° or less. More specifically, the first angle θ is approximately 27° at an angle of view of 50°. In this case, by setting the first angle θ, for example, so that the first angle θ is 30° or less (for example, approximately 27°), distortion aberration is suppressed, and, as can be seen, this allows the virtual image display apparatus  100  without or with very minimal circuit correction to be achieved. 
     Furthermore, a point PP2 indicates an example of the present embodiment (second embodiment), in other words, a case where the vertical distortion has been corrected. In this case also, the first angle θ is greater than 0° and 45° or less. More specifically, for example, the first angle θ is approximately 35° at an angle of view of 50° or 60°. Also, the first angle θ is approximately from 37° to 38° (less than 40°) at an angle of view of 40° or 45°. As seen from these, in the case of the present embodiment (second embodiment), when the first angle θ is kept in a range from 35° to 40°, the virtual image display apparatus  100  can reduce the burden of circuit correction and can form an image with a wide angle of view including an angle of view from 40° to 60°. That is, in the present embodiment (second embodiment), the first angle θ is in a range from 35° to 40°, and the correction of distortion aberration of the image for the direction (vertical direction of the image) corresponding to the light guiding (light guiding in the −Y direction) by the first mirror  21 , the refractive reflective optical member  22 , and the second mirror  23  is larger than the correction for the direction (horizontal direction of image) perpendicular to this direction. Thus, the burden of aberration correction can be reduced, and an increase in the size of the apparatus and the like can be suppressed. 
     Modified Examples and Others 
     The present disclosure is described according to the above-described embodiments, but the present disclosure is not limited to the above-described embodiments. The present disclosure may be implemented in various modes without departing from the gist of the present disclosure, and, for example, the following modifications may be carried out. 
     In the virtual image display apparatus  100  in the above-described embodiments, a self-luminous type display element such as an organic EL element is used as the display device  11 . However, a configuration in which a laser scanner obtained by combining a laser light source and a scanner such as a polygon mirror may instead be used as the display device  11 . That is, it is also possible to apply the present disclosure to a laser retinal projection type head-mounted display. 
     The mirror portion  22   r  of the refractive reflective optical member  22  is not limited to being formed of the reflection film  22   c  and may be a total reflection surface that satisfies total reflection conditions. 
     A light control device that controls light by limiting transmitted light of the second mirror  23  may be attached to the external side of the second mirror  23 . The light control device adjusts a transmittance, for example, electrically. Mirror liquid crystals, electronic shades, and the like may be used as the light control device. The light control device may adjust a transmittance according to outside light brightness. When the light control device blocks the external light OL, only a virtual image that is not affected by an external image can be observed. Further, the virtual image display apparatus of the claimed disclosure is applicable to a so-called closed-type head-mounted display device (HMD) that blocks external light and causes only imaging light to be visually recognized. In this case, the HMD may also be compatible with a so-called see-through video product constituted by a virtual image display apparatus and an imaging device. 
     The reflection film  23   c  of the second mirror  23  is not limited to having semi-transmissive properties and may be configured to reflect a specific polarization component such as a wire grid element. The reflection film  23   c  of the second mirror  23  may also be constituted by a volume hologram or the other hologram element, or may also be constituted by a diffraction grating. 
     In the description above, the virtual image display apparatus  100  is assumed to be mounted and used on a head, but the virtual image display apparatus  100  described above may also be used as a hand-held display that is not mounted on a head and is viewed into it like a pair of binoculars. In other words, the head-mounted display also includes a hand-held display in the present disclosure. 
     The virtual image display apparatus according to a specific mode includes: an imaging light emitting unit configured to emit an imaging light; a first mirror configured to reflect the imaging light from the imaging light emitting unit; an optical member including a reflecting portion configured to reflect the imaging light reflected by the first mirror; and a second mirror configured to reflect the imaging light reflected by the reflecting portion toward a position of an exit pupil, wherein a distance from the imaging light emitting unit to the first mirror is shorter than a distance from the position of the exit pupil to the second mirror; and a first angle formed by the imaging light incident on the second mirror and the imaging light reflected by the second mirror is greater than 0° and 45° or less. 
     In the virtual image display apparatus, the distance from the position of the exit pupil to the second mirror is provided and the first angle formed by the imaging light incident on the second mirror and the imaging light reflected by the second mirror is 45° or less. This allows the occurrence of image distortion to be sufficiently suppressed, and allows for image formation with high accuracy to be performed without requiring electrical correction and the like by a correction circuit, for example. 
     In a specific aspect, the optical member includes an incidence-emission portion where the imaging light from the first mirror is incident and where the imaging light reflected by the reflecting portion is emitted; and the incidence-emission portion is configured to refract the imaging light incident and the imaging light emitted. In this case, optical path adjustment is possible in relation to the refraction effects of a refractive reflective optical member. 
     In a specific aspect, the incidence-emission portion is an aspheric surface or a free curved surface. In this case, distortion aberration can be suppressed at the refractive reflective optical member. 
     In a specific aspect, a distance C from the position of the exit pupil to the second mirror is represented by a following formula: 
     
       
         
           
             C 
             = 
             
               
                 y 
                 + 
                 
                   z 
                   * 
                   tan 
                   ⁢ 
                      
                   
                     ( 
                     
                       θ 
                       + 
                       α 
                     
                     ) 
                   
                 
               
               
                 
                   cos 
                   ⁢ 
                      
                   
                     ( 
                     α 
                     ) 
                   
                   * 
                   tan 
                   ⁢ 
                      
                   
                     ( 
                     
                       θ 
                       + 
                       α 
                     
                     ) 
                   
                 
                 - 
                 
                   sin 
                   ⁢ 
                      
                   
                     ( 
                     α 
                     ) 
                   
                 
               
             
           
         
       
     
     where 
     y is a distance in a vertical direction from the position of the exit pupil to a position of the optical member when a user normally wears the virtual image display apparatus, 
     z is a distance in a horizontal direction from the position of the exit pupil to the position of the optical member when the user normally wears the virtual image display apparatus, 
     α is an inclination angle of a line-of-sight of the user with respect to the horizontal direction, and 
     θ is the first angle. In this case, a balance with the distance C can be achieved, allowing an increase in the size of the apparatus to be avoided and aberration suppressed. 
     In a specific aspect, the first angle is 30° or less. In this case, for example, for a rectangular image, aberration can be sufficiently suppressed in both the vertical direction and the horizontal direction. 
     In a specific aspect, the first angle is in a range from 35° to 40°; and in an image formed by the imaging light, distortion occurring in a direction corresponding to light guiding of the imaging light by the first mirror, the optical member, and the second mirror is larger than distortion occurring in a direction different to the direction. In this case, an increase in the size of the apparatus can be suppressed, and aberration in a direction with a greater effect can be suppressed. 
     In a specific aspect, the first angle is less than a second angle formed by the imaging light incident on the first mirror and the imaging light reflected by the first mirror. In this case, because the first angle is sufficiently small, an overall optical system with suppressed aberration is achieved. 
     In a specific aspect, the first mirror, the second mirror, and the reflecting portion are each an aspheric surface or a free curved surface. In this case, aberration can be suppressed at each reflection surface. 
     In a specific aspect, the second mirror is configured to reflect a portion of the imaging light toward the position of the exit pupil and transmits another portion of the imaging light. In this case, see-through viewing is possible.