Image display apparatus

• US 5,986,812 A
• Filed: 07/18/1997
• Issued: 11/16/1999
• Est. Priority Date: 07/19/1996
• Status: Expired due to Term

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Takahashi, Junko
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): MACK, RICKY LEVERN
• Application Number:
  US08/896,856
• Time in Patent Office: 851 Days
• Field of Search: 359/630, 359/631, 359/633, 359/637, 359/638, 359/639, 359/640
• US Class Current: 359/630
• CPC Class Codes: G02B 2027/011 comprising device for correcting geometrical aberrations, distortion
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• CPC Class Codes: G02B 27/0172 characterised by optical features

Abstract

A head-mounted image display apparatus capable of providing an observation image which is clear and has minimal distortion even at a wide field angle. Display light from an image display device (7) enters an optical system (8) through a first surface (3) serving as both transmitting and reflecting surfaces. The incident light is reflected by a third surface (5) and further reflected by the first surface (3). Then, the reflected light is reflected by a second surface 4 which is a decentered reflecting surface disposed on an optical axis (2) to face an exit pupil (1). The reflected light exits from the optical system (8) through the first surface (3), travels along the optical axis (2) and enters an observer'"'"'s pupil placed at the exit pupil (1), without forming an intermediate image, thus forming a display image on the retina of the observer'"'"'s eye. The first to third surfaces (3 to 5) are each formed from a plane-symmetry three-dimensional surface having no axis of rotational symmetry in nor out of the surface and having only one plane of symmetry.

Claims

1. An image display apparatus, comprising:

an image display device; and

an ocular optical system for leading an image formed by said image display device to a position of an eyeball of an observer without forming an intermediate image so that the image is observed as a virtual image,

wherein said ocular optical system includes a prism member,

said prism member having at least two surfaces having a reflecting action, said at least two surfaces being arranged such that light rays entering said prism member are internally reflected at least three times,

wherein at least one of said at least two surfaces having a reflecting action is formed from a curved surface, and

wherein said curved surface is a plane-symmetry three-dimensional surface with a rotationally asymmetric surface configuration having only one plane of symmetry.

2. An image display apparatus according to claim 1, wherein the surface configuration of said plane-symmetry three-dimensional surface is expressed by the following defining equation:

##EQU4## wherein C₂, C₃, C₄, C₅, C₆, C₇, C₈, C₉, C₁₀, C₁₁, C₁₂, C₁₃, C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, C₁₉, C₂₀, C₂₁, C₂₂, C₂₃, C₂₄, C₂₅, C₂₆, C₂₇, C₂₈, C₂₉, C₃₀, C₃₁, C₃₂, C₃₃, C₃₄, C₃₅, C₃₆, and C₃₇ are constant coefficients of coordinates x and y that are selectable,

wherein x, y and z are Cartesian coordinates, along the X-axis, Y-axis, and Z-axis, respectively;

wherein said plane-symmetry three-dimensional surface has only one plane of symmetry parallel to a YZ-plane, said plane-symmetry three-dimensional surface being obtained by setting coefficients of all terms with odd-numbered powers of x in the defining equation equal to zero, or

said plane-symmetry three-dimensional surface has only one plane of symmetry parallel to an XZ-plane, said plane-symmetry three-dimensional surface being obtained by setting coefficients of all terms with odd-numbered powers of y in the defining equation equal to zero.

4. An image display apparatus according to claim 1, wherein said prism member has at least three optical surfaces that reflect and/or transmit light emitted from said image display device.

5. An image display apparatus according to claim 4, wherein said prism member has four optical surfaces that reflect and/or transmit light emitted from said image display device.

6. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.05<

|CX2/CY2|<

8

where CY2 and CX2 denote curvatures in Y- and X-axis directions, respectively, of that portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

7. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|DY52|<

0.1

where DY52 denotes DY5-DY2 when a Y-axis direction is defined as a vertical direction, and DY2 and DY5 are tilts of an equation defining a configuration of said reflecting surface in a Y-axis direction, which corresponds to a decentering direction of said surface, at portions of said reflecting surface which are struck by an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field and a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, respectively.

8. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CXyy|<

0.1 (1/millimeter)

where CXyy denotes each value of differences CX3-CX1 and CX6-CX4 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

9. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.001<

|CX2| (1/millimeter)

where CX2 denotes a curvature in an X-axis direction of a portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

10. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.001<

|CY2| (1/millimeter)

where CY2 denotes a curvature in a Y-axis direction of a portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

11. An image display apparatus according to claim 4,

wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">-0.05<

CXn2<

0.05 (1/millimeter)

where CXn2 denotes each value of differences CXn-CX2, wherein n has a value of 1, 3, 4, 5 or 6 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

12. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYn2|<

0.05 (1/millimeter)

where CYn2 denotes each value of differences CYn-CY2, wherein n has a value of 1, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

13. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">CXYM<

100

where CXYM denotes |CXn|/|CYn|, wherein n has a value of 1, 2, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively, and further curvatures in a Y-axis direction, which corresponds to the decentering direction, of the equation at said points in said effective area are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

14. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and all reflecting surfaces constituting said ocular optical system satisfy the following condition:

space="preserve" listing-type="equation">CXYA<

100

where CXYA denotes |CXn|/|CYn|, wherein n has a value of 1, 2, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively, and further curvatures in a Y-axis direction, which corresponds to the decentering direction, of the equation at said points in said effective area are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

15. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">-0.2<

DX46<

0.2

where DX46 denotes DX4-DX6 when a Y-axis direction is defined as a vertical direction, and DX4 and DX6 are tilts of an equation defining a configuration of said reflecting surface in an X-axis direction, which perpendicularly intersects a decentering direction of said surface, at portions of said reflecting surface which are struck by a principal ray (4) in a field angle direction corresponding to an upper-right corner of an image field and a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, respectively.

16. An image display apparatus according to claim 4, wherein a Z-axis is taken in a prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CXx0|<

0.1 (1/millimeter)

where CXx0 denotes each value of CX4-CX1, CX5-CX2 and CX6-CX3 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

17. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYx0|<

0.1 (1/millimeter)

where CYx0 denotes each value of CY4-CY1, CY5-CY2 and CY6-CY3 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

18. An image display apparatus according to claim 4, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYyy|<

0.1 (1/millimeter)

where CYyy denotes each value of CY3-CY1 and CY6-CY4 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

3. A head-mounted image display apparatus comprising:

an image display apparatus, comprising;

an image display device, and

an ocular optical system for leading an image formed by said image display device to a position of an eyeball of an observer without forming an intermediate image so that the image can be observed as a virtual image,

a body unit covering said image display apparatus; and

a support member provided on said body unit to support said body unit on an observer'"'"'s head,

wherein said ocular optical system includes a prism member,

said prism member having at least two surfaces having a reflecting action, said at least two surfaces being arranged such that light rays entering said prism member are internally reflected at least three times,

wherein at least one of said at least two surfaces having a reflecting action is formed from a curved surface, and

wherein said curved surface is a plane-symmetry three-dimensional surface with a rotationally asymmetric surface configuration having only one plane of symmetry.

19. A head-mounted image display apparatus according to claim 3,

wherein said prism member has at least three optical surfaces that reflect and/or transmit light emitted from said image display device.

20. A head-mounted image display apparatus according to claim 19, wherein said prism member has four optical surfaces that reflect and/or transmit light emitted from said image display device.

21. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.05<

|CX2/CY2|<

8

where CY2 and CX2 denote curvatures in Y- and X-axis directions, respectively, of that portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

22. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|DY52|<

0.1

where DY52 denotes DY5-DY2 when a Y-axis direction is defined as a vertical direction, and DY2 and DY5 are tilts of an equation defining a configuration of said reflecting surface in a Y-axis direction, which corresponds to a decentering direction of said surface, at portions of said reflecting surface which are struck by an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field and a principal ray (5) in a field tingle direction corresponding to a center of a right-hand edge of the image field, respectively.

23. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CXyy|<

0.1 (1/millimeter)

where CXyy denotes each value of differences CX3-CX1 and CX6-CX4 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

24. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.001<

|CX2| (1/millimeter)

where CX2 denotes a curvature in an X-axis direction of a portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

25. A head-mounted image display apparatus according to claim 19, wherein, a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0.001<

|CY2| (1/millimeter)

where CY2 denotes a curvature in a Y-axis direction of a portion of said reflecting surface which is struck by an axial principal ray passing through a center of an exit pupil of said ocular optical system and reaching a center of an image to be observed.

26. A head-mounted image display apparatus according to claim 19,

wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">-0.05<

CXn2<

0.05 (1/millimeter)

where CXn2 denotes each value of difference CXn-CX2, wherein n has a value of 1, 3, 4, 5 or 6 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

27. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYn2|<

0.05 (1/millimeter)

where CYn2 denotes each value of differences CYn-CY2, wherein n has a value of 1, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1) to (6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

28. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and a reflecting surface having a strongest reflective refracting power of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">CXYM<

100

where CXYM denotes |CXn|/|CYn|, wherein n has a value of 1, 2, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively, and further curvatures in a Y-axis direction, which corresponds to the decentering direction, of the equation at said points in said effective area are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

29. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and all reflecting surfaces constituting said ocular optical system satisfy the following condition:

space="preserve" listing-type="equation">CXYA<

100

where CXYA denotes |CXn|/|CYn|, wherein n has a value of 1, 2, 3, 4, 5 or 6, when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively, and further curvatures in a Y-axis direction, which corresponds to the decentering direction, of the equation at said points in said effective area are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

30. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">-0.2<

DX46<

0.2

where DX46 denotes DX4-DX6 when a Y-axis direction is defined as a vertical direction, and DX4 and DX6 are tilts of an equation defining a configuration of said reflecting surface in an X-axis direction, which perpendicularly intersects a decentering direction of said surface, at portions of said reflecting surface which are struck by a principal ray (4) in a field angle direction corresponding to an upper-right corner of an image field and a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, respectively.

31. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CXx0|<

0.1 (1/millimeter)

where CXx0 denotes each value of CX4-CX1, CX5-CX2 and CX6-CX3 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in an X-axis direction, which perpendicularly intersects a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CX1, CX2, CX3, CX4, CX5, and CX6, respectively.

32. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYx0|<

0.1 (1/millimeter)

where CYx0 denotes each value of CY4-CY1, CY5-CY2 and CY6-CY3 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.

33. A head-mounted image display apparatus according to claim 19, wherein a Z-axis is taken in a direction of prolongation of a line segment along which an axial principal ray from a center of an image display area of said image display device travels to reach a center of said observer'"'"'s eyeball position after exiting from said ocular optical system, a Y-axis is taken in a direction perpendicular to said Z-axis in a plane containing a folded line segment along which said axial principal ray is reflected by said reflecting surfaces, an X-axis is taken in a direction perpendicular to both said Z- and Y-axes, and at least one of said reflecting surfaces constituting said ocular optical system satisfies the following condition:

space="preserve" listing-type="equation">0<

|CYyy|<

0.1 (1/millimeter)

where CYyy denotes each value of CY3-CY1 and CY6-CY4 when an effective area is defined for each surface as being an area formed by intersection of the surface and six principal rays, which are, with a Y-axis direction defined as a vertical direction, an axial principal ray (2) in a Z-axis direction corresponding to a center of an image field, a principal ray (1) in a field angle direction corresponding to a center of an upper edge of the image field, a principal ray (4) in a field angle direction corresponding to an upper-right corner of the image field, a principal ray (5) in a field angle direction corresponding to a center of a right-hand edge of the image field, a principal ray (6) in a field angle direction corresponding to a lower-right corner of the image field, and a principal ray (3) in a field angle direction corresponding to a center of a lower edge of the image field, and curvatures in a Y-axis direction, which corresponds to a decentering direction, of an equation defining a configuration of the surface at points in said effective area at which said six principal rays (1 to

     6) strike the surface are defined as CY1, CY2, CY3, CY4, CY5, and CY6, respectively.