U.S. patent number RE37,579 [Application Number 09/383,382] was granted by the patent office on 2002-03-12 for image display apparatus comprising an internally reflecting ocular optical system.
This patent grant is currently assigned to Olympus Optical Co., Ltd.. Invention is credited to Koichi Takahashi.
United States Patent |
RE37,579 |
Takahashi |
March 12, 2002 |
Image display apparatus comprising an internally reflecting ocular
optical system
Abstract
An image display apparatus which enables observation of a clear
image at a wide field angle with substantially no reduction in the
brightness of the observation image, and which is extremely small
in size and fight in weight and hence unlikely to cause the
observer to be fatigued. The image display apparatus includes an
image display device and an ocular optical system for projecting an
image formed by the image display device and for leading the
projected image to an observer's eyeball. The ocular optical system
(3) has three surfaces, and a space formed by the three surfaces is
filled with a medium having a refractive index larger than 1. The
three surfaces include, in the order in which light rays pass in
backward ray tracing from the observer's eyeball (1) to the image
display device (4), a first surface (5) which functions as both a
refracting surface and an internally reflecting surface, a second
surface (6) which is a reflecting surface facing the first surface
(5) and decentered or tilted with respect to an observer's visual
axis (2), and a third surface (7) which is a refracting surface
closest to the image display device (4), so that reflection takes
place three times in the path from the observer's eyeball (1) to
the image display device (4).
Inventors: |
Takahashi; Koichi (Hachioji,
JP) |
Assignee: |
Olympus Optical Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
12157620 |
Appl.
No.: |
09/383,382 |
Filed: |
August 26, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
605886 |
Feb 23, 1996 |
05699194 |
Dec 16, 1997 |
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Foreign Application Priority Data
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Feb 13, 1996 [JP] |
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8-025138 |
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Current U.S.
Class: |
359/633; 359/631;
359/637 |
Current CPC
Class: |
G02B
27/0101 (20130101); G02B 27/0172 (20130101); G02B
2027/011 (20130101); G02B 2027/0118 (20130101); G02B
2027/0125 (20130101); G02B 2027/0132 (20130101); G02B
2027/0178 (20130101) |
Current International
Class: |
G02B
27/01 (20060101); G02B 27/00 (20060101); G02B
027/14 () |
Field of
Search: |
;359/630,631,633,636,637,639,640 ;345/7,8 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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365406 |
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Apr 1990 |
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EP |
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408 344 |
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Jan 1991 |
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EP |
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460 983 |
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Dec 1991 |
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EP |
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583 116 |
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Feb 1994 |
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EP |
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687 932 |
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Dec 1995 |
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EP |
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3-101709 |
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Apr 1991 |
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JP |
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6-242393 |
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Sep 1994 |
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JP |
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7-333505 |
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Dec 1995 |
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JP |
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7-333551 |
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Dec 1995 |
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JP |
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Primary Examiner: Mack; Ricky
Attorney, Agent or Firm: Pillsbury Winthrop LLP
Claims
What we claim is: .[.
1. An image display apparatus comprising an image display device
for displaying an image, and an ocular optical system for
projecting the image formed by said image display device and for
leading the projected image to an observer's eyeball,
said ocular optical system being arranged such that light rays
emitted from said image display device are reflected three or
higher odd-numbered times before reaching said observer's eyeball,
and that a surface of said ocular optical system that is disposed
immediately in front of said observer's eyeball is a refracting
surface which internally reflects the light rays, and through which
the light rays exit from said ocular optical system..]. .[.
2. An image display apparatus comprising an image display device
for displaying an image, and an ocular optical system for
projecting the image formed by said image display device and for
leading the projected image to an observer's eyeball,
said ocular optical system being arranged such that light rays
emitted from said image display device are reflected three times
before reaching said observer's eyeball, and that a surface of said
ocular optical system that is disposed immediately in front of said
observer's eyeball is a refracting surface which internally
reflects the light rays, and through which the light rays exit from
said ocular optical system..].
3. An image display apparatus comprising an image display device
for displaying an image, and an ocular optical system for
projecting the image formed by said image display device and for
leading the projected image to an observer's eyeball,
said ocular optical system having at least three surfaces, wherein
a space formed by said at least three surfaces is filled with a
medium having a refractive index larger than 1,
said at least three surfaces including, in an order in which light
rays pass in backward ray tracing from said observer's eyeball to
said image display device, a first surface which functions as both
a refracting surface and an internally reflecting surface, a second
surface which is a reflecting surface facing said first surface and
decentered or tilted with respect to an observer's visual axis, and
a third surface which is a refracting surface closest to said image
display device, so that reflection takes place three times in a
path from said observer's eyeball to said image display device.
4. An image display apparatus comprising an image display device
for displaying an image, and an ocular optical system for
projecting the image formed by said image display device and for
leading the projected image to an observer's eyeball,
said ocular optical system having at least four surfaces, wherein a
space formed by said at least four surfaces is filled with a medium
having a refractive index larger than 1,
said at least four surfaces including, in an order in which light
rays pass in backward ray tracing from said observer's eyeball to
said image display device, a first surface which functions as both
a refracting surface and an internally reflecting surface, a second
surface which is a reflecting surface facing said first surface and
decentered or tilted with respect to an observer's visual axis, a
third surface which is a reflecting surface facing said first
surface and adjacent to said second surface, and a fourth surface
which is a refracting surface closest to said image display device,
so that reflection takes place three times in a path from said
observer's eyeball to said image display device.
5. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, wherein at least one of the
surfaces constituting said ocular optical system is a flat
surface.
6. An image display apparatus according to claim 3 or 4, wherein
the internal reflection at said first surface is total
reflection.
7. An image display apparatus according to any one of claims 3 or
4, wherein said second surface is a reflecting surface which is
concave toward said first surface.
8. An image display apparatus according to any one of claims 3 or
4, wherein said first surface is a surface which functions as both
a transmitting surface and a reflecting surface, said first surface
being convex toward said second surface.
9. An image display apparatus according to any one of claims 3 or
4, wherein said first surface is a flat surface which functions as
both a transmitting surface and a reflecting surface.
10. An image display apparatus according to claim 3 or 4, wherein
an internally reflecting region of said first surface has a
reflective coating.
11. An image display apparatus according to claim 3 or 4 wherein
said first surface is a surface which functions as both a
transmitting surface and a reflecting surface, said first surface
being concave toward said second surface.
12. An image display apparatus according to claim 3 or 4, wherein
said second surface is a reflecting surface which is convex toward
said first surface.
13. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.2 is an incident angle of an axial principal
ray at a first reflection by said second surface in the backward
ray tracing.
14. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.2 is an incident angle of an axial principal
ray at a first reflection by said second surface in the backward
ray tracing.
15. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.1 is an incident angle of an axial principal
ray at said first surface.
16. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.1 is an incident angle of an axial principal
ray at said first surface.
17. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.3 is an incident angle of an axial principal
ray at internal reflection by said first surface.
18. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.3 is an incident angle of an axial principal
ray at internal reflection by said first surface.
19. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.4 is an incident angle of an axial principal
ray when reflected for a second time in the backward ray tracing by
said second surface of said ocular optical system comprising three
surfaces, or .theta..sub.4 is an incident angle of an axial
principal ray at said third surface of said ocular optical system
comprising four surfaces.
20. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.4 is an incident angle of an axial principal
ray when reflected for a second time in the backward ray tracing by
said second surface of said ocular optical system comprising three
surfaces, or .theta..sub.4 is an incident angle of an axial
principal ray at said third surface of said ocular optical system
comprising four surfaces.
21. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
-30.degree.<.theta..sub.5 <40.degree. (9)
wherein .theta..sub.5 is an incident angle of an axial principal
ray at said third surface in said ocular optical system comprising
three surfaces, or .theta..sub.5 is an incident angle of an axial
principal ray at said fourth surface in said ocular optical system
comprising four surfaces.
22. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.i is an incident angle of an axial principal
ray at a display surface of said image display device.
23. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
wherein .theta..sub.i is an incident angle of an axial principal
ray at a display surface of said image display device.
24. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1.
25. An image display apparatus according to claim 3 or 4, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1.
26. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, wherein at least one of the
surfaces constituting said ocular optical system is an aspherical
surface.
27. An image display apparatus according to claim 26, wherein at
least one of the surfaces constituting said ocular optical system
is an anamorphic surface.
28. An image display apparatus according to claim 26, wherein at
least one of the surfaces constituting said ocular optical system
is a free curved surface.
29. An image display apparatus according to claim 3 or 4, wherein a
display surface of said image display device is tilted with respect
to an axial principal ray.
30. An image display apparatus according to claim 29, wherein said
image display device is disposed in such a manner that a side
thereof which is reverse to said display surface faces said
observer.
31. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, further comprising means for
positioning both said image display device and said ocular optical
system with respect to the observer's head.
32. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, further comprising means for
supporting both said image display device and said ocular optical
system with respect to the observer's head.
33. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, further comprising means for
supporting at least a pair of said image display apparatuses at a
predetermined spacing.
34. An image display apparatus according to .[.any one of claims 1
to .]. .Iadd.claim 3 or .Iaddend.4, wherein said ocular optical
system is used as an imaging optical system..Iadd.
35. An imaging optical system wherein a light beam from an object
is passed through a pupil to form an object image on an image
plane, said imaging optical system comprising:
at least an optical member for one of converging and diverging the
light beam,
said optical member being provided between said pupil and said
image plane,
said optical member having at least three surfaces, wherein a space
formed by said at least three surfaces is filled with a medium
having a refractive index larger than 1,
said at least three surfaces including, in an order in which light
rays pass in ray tracing from said pupil to said image plane, a
first surface which functions as both a refracting surface and an
internally reflecting surface, a second surface which is a
reflecting surface facing said first surface and decentered or
tilted, and a third surface which is a refracting surface closest
to said image plane, so that reflection takes place three times in
a path from said pupil to said image plane..Iaddend..Iadd.
36. An imaging optical system wherein a light beam from an object
is passed through a pupil to form an object image on an image
plane, said imaging optical system comprising:
at least an optical member for one of converging and diverging the
light beam,
said optical member being provided between said pupil and said
image plane,
said optical member having at least four surfaces, wherein a space
formed by said at least four surfaces is filled with a medium
having a refractive index larger than 1,
said at least four surfaces including, in an order in which light
rays pass in ray tracing from said pupil to said image plane, a
first surface which functions as both a refracting surface and an
internally reflecting surface, a second surface which is a
reflecting surface facing said first surface and decentered or
tilted, a third surface which is a reflecting surface facing said
first surface and adjacent to said second surface, and a fourth
surface which is a refracting surface closest to said image plane,
so that reflection takes place three times in a path from said
pupil to said image plane..Iaddend..Iadd.
37. A finder optical system comprising:
the imaging optical system of claim 35 or 36;
an imaging erecting optical system for erecting the object image
formed on said image plane by said imaging optical system; and
an ocular optical system for viewing said object
time..Iaddend..Iadd.
38. A camera apparatus comprising:
the imaging optical system of claim 35 or 36, said imaging optical
system being incorporated as an optical system for forming an
object image..Iaddend..Iadd.
39. An imaging optical system according to claim 35 or 36, wherein
at least one of the surfaces constituting said optical member is a
flat surface..Iaddend..Iadd.
40. An imaging optical system according to claim 35 or 36, wherein
the internal reflection at said first surface is total
reflection..Iaddend..Iadd.
41. An imaging optical system according to claim 35 or 36, wherein
said second surface is a reflecting surface which is concave toward
said first surface..Iaddend..Iadd.
42. An imaging optical system according to claim 35 or 36, wherein
said first surface is a surface which functions as both a
transmitting surface and a reflecting surface, said first surface
being convex toward said second surface..Iaddend..Iadd.
43. An imaging optical system according to claim 35 or 36, wherein
said first surface is a flat surface which functions as both a
transmitting surface and a reflecting surface..Iaddend..Iadd.
44. An imaging optical system according to claim 35 or 36, wherein
an internally reflecting region of said first surface has a
reflective coating..Iaddend..Iadd.
45. An imaging optical system according to claim 35 or 36, wherein
said first surface is a surface which functions as both a
transmitting surface and a reflecting surface, said first surface
being concave toward said second surface..Iaddend..Iadd.
46. An imaging optical system according to claim 35 or 36, wherein
said second surface is a reflecting surface which is convex toward
said first surface..Iaddend..Iadd.
47. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.2 is an incident angle of an axial principal ray
at a first reflection by said second surface in the ray
tracing..Iaddend..Iadd.
48. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.2 is an incident angle of an axial principal ray
at a first reflection by said second surface in the ray
tracing..Iaddend..Iadd.
49. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.1 is an incident angle of an axial principal ray
at said first surface..Iaddend..Iadd.
50. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.1 is an incident angle of an axial principal ray
at said first surface..Iaddend..Iadd.
51. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.3 is an incident angle of an axial principal ray
at internal reflection by said first surface..Iaddend..Iadd.
52. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.3 is an incident angle of an axial principal ray
at internal reflection by said first surface..Iaddend..Iadd.
53. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.4 is one of (1) an incident angle of an axial
principal ray when reflected for a second time in the ray tracing
by said second surface of said optical member comprising three
surfaces, and (2) an incident angle of an axial principal ray at
said third surface of said optical member comprising four
surfaces..Iaddend..Iadd.
54. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.4 is one of (1) an incident angle of an axial
principal ray when reflected for a second time in the ray tracing
by said second surface of said optical member comprising three
surfaces, and (2) an incident angle of an axial principal ray at
said third surface of said optical member comprising four
surfaces..Iaddend..Iadd.
55. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.5 is one of (1) an incident angle of an axial
principal ray at said third surface in said optical member
comprising three surfaces, and (2) an incident angle of an axial
principal ray at said fourth surface in said optical member
comprising four surfaces..Iaddend..Iadd.
56. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.i is an incident angle of an axial principal ray
on said image plane..Iaddend..Iadd.
57. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where .theta..sub.i incident angle of an axial principal ray on
said image plane..Iaddend..Iadd.
58. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1..Iaddend..Iadd.
59. An imaging optical system according to claim 35 or 36, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1..Iaddend..Iadd.
60. An imaging optical system according to claim 35 or 36, wherein
at least one of the surfaces constituting said optical member is an
aspherical surface..Iaddend..Iadd.
61. An imaging optical system according to claim 60, wherein at
least one of the surfaces constituting said optical member is an
anamorphic surface..Iaddend..Iadd.
62. An imaging optical system according to claim 35 or 36, wherein
a front optical system is placed on an object side of said
pupil..Iaddend..Iadd.
63. An imaging optical system according to claim 35 or 36, wherein
said image plane is tilted with respect to an axial principal
ray..Iaddend..Iadd.
64. A viewing optical system comprising:
image-forming means for forming an observation image on an image
plane, and
an ocular optical system for projecting said observation image and
for leading the projected image to an observer's eyeball,
said ocular optical system having at least three surfaces, wherein
a space formed by said at least three surfaces is filled with a
medium having a refractive index larger than 1,
said at least three surfaces including, in an order in which light
rays pass in backward ray tracing from said observer's eyeball to
said observation image, a first surface which functions as both a
refracting surface and an internally reflecting surface, a second
surface which is a reflecting surface facing said first surface and
decentered or tilted with respect to an observer's visual axis, and
a third surface which is a refracting surface closest to said
observation image, so that reflection takes place three times in a
path from said observer's eyeball to said observation
image..Iaddend..Iadd.
65. A viewing optical system comprising:
image-forming means for forming an observation image on an image
plane, and
an ocular optical system for projecting said observation image and
for leading the projected image to an observer's eyeball,
said ocular optical system having at least four surfaces, wherein a
space formed by said at least four surfaces is filled with a medium
having a refractive index larger than 1,
said at least four surfaces including, in an order in which light
rays pass in backward ray tracing from said observer's eyeball to
said observation image, a first surface which functions as both a
refracting surface and an internally reflecting surface, a second
surface which is a reflecting surface facing said first surface and
decentered or tilted with respect to an observer's visual axis, a
third surface which is a reflecting surface facing said first
surface and adjacent to said second surface, and a fourth surface
which is a refracting surface closest to said observation image, so
that reflection takes place three times in a path from said
observer's eyeball to said observation image..Iaddend..Iadd.
66. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1..Iaddend..Iadd.
67. A viewing optical system according to claim 64 or 65, wherein
at least one of the surfaces constituting said ocular optical
system is an aspherical surface..Iaddend..Iadd.
68. A viewing optical system according to claim 67, wherein at
least one of the surfaces constituting said ocular optical system
is an anamorphic surface..Iaddend..Iadd.
69. A viewing optical system according to claim 67, wherein at
least one of the surfaces constituting said ocular optical system
is a free curved surface..Iaddend..Iadd.
70. A viewing optical system according to claim 64 or 65, wherein
an image surface of said observation image formed by said
image-forming means is tilted with respect to an axial principal
ray..Iaddend..Iadd.
71. A viewing optical system according to claim 64 or 65, wherein
at least one of the surfaces constituting said ocular optical
system is a flat surface..Iaddend..Iadd.
72. A viewing optical system according to claim 64 or 65, wherein
the internal reflection at said first surface is total
reflection..Iaddend..Iadd.
73. A viewing optical system according to claim 64 or 65, wherein
said second surface is a reflecting surface which is concave toward
said first surface..Iaddend..Iadd.
74. A viewing optical system according to claim 64 or 65, wherein
said first surface is a surface which functions as both a
transmitting surface and a reflecting surface, said first surface
being convex toward said second surface..Iaddend..Iadd.
75. A viewing optical system according to claim 64 or 65, wherein
said first surface is a flat surface which functions as both a
transmitting surface and a reflecting surface..Iaddend..Iadd.
76. A viewing optical system according to claim 64 or 65, wherein
an internally reflecting region of said first surface has a
reflective coating..Iaddend..Iadd.
77. A viewing optical system according to claim 64 or 65, wherein
said first surface is a surface which functions as both a
transmitting surface and a reflecting surface, said first surface
being concave toward said second surface..Iaddend..Iadd.
78. A viewing optical system according to claim 64 or 65, wherein
said second surface is a reflecting surface which is convex toward
said first surface..Iaddend..Iadd.
79. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.2 is an incident angle of an axial principal ray
at a first reflection by said second surface in the backward ray
tracing..Iaddend..Iadd.
80. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.2 is an incident angle of an axial principal ray
at a first reflection by said second surface in the backward ray
tracing..Iaddend..Iadd.
81. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.1 is an incident angle of an axial principal ray
at said first surface..Iaddend..Iadd.
82. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.1 is an incident angle of an axial principal ray
at said first surface..Iaddend..Iadd.
83. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.3 is an incident angle of an axial principal ray
at internal reflection by said first surface..Iaddend..Iadd.
84. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.3 is an incident angle of an axial principal ray
at internal reflection by said first surface..Iaddend..Iadd.
85. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
20.degree.<.theta..sub.4 <80.degree. (7)
where .theta..sub.4 is one of (1) an incident angle of an axial
principal ray when reflected for a second time in the backward ray
tracing by said second surface of said ocular optical system
comprising three surfaces, and (2) an incident angle of an axial
principal ray at said third surface of said ocular optical system
comprising four surfaces..Iaddend..Iadd.
86. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.4 is one of (1) an incident angle of an axial
principal ray when reflected for a second time in the backward ray
tracing by said second surface of said ocular optical system
comprising three surfaces, and (2) an incident angle of an axial
principal ray at said third surface of said ocular optical system
comprising four surfaces..Iaddend..Iadd.
87. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.5 is one of an incident angle of an axial
principal ray at said third surface in said ocular optical system
comprising three surfaces, and (2) an incident angle of an axial
principal ray at said fourth surface in said ocular optical system
comprising four surfaces..Iaddend..Iadd.
88. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.i is an incident angle of an axial principal ray
on a surface of said observation image..Iaddend..Iadd.
89. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where .theta..sub.i is an incident angle of an axial principal ray
on a surface of said observation image..Iaddend..Iadd.
90. A viewing optical system according to claim 64 or 65, which
satisfies the following condition:
where N.sub.d is a refractive index for the spectral d-line of said
medium having a refractive index larger than 1..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an image display apparatus and,
more particularly, to a head- or face-mounted image display
apparatus that can be retained on the observer's head or face.
As an example of conventional head- or face-mounted image display
apparatus, an image display apparatus disclosed in Japanese Patent
Application Unexamined Publication (KOKAI) No. 3-101709 (1991) is
known. FIG. 20 shows the optical system of the conventional image
display apparatus. As illustrated in the figure, in the
conventional image display apparatus, an image that is displayed by
an image display device is transmitted as an aerial image by a
relay optical system including a positive lens, and the aerial
image is projected into an observer's eyeball as an enlarged image
by an ocular optical system formed from a concave reflecting
mirror.
Japanese Patent Application Unexamined Publication (KOKAI) No.
62-214782 (1987) discloses another type of conventional image
display apparatus. As shown in FIGS. 21(a) and 21(b), the
conventional image display apparatus is designed to enable an image
of an image display device to be directly observed as an enlarged
image through an ocular lens.
U.S. Pat. No. 4,026,641 discloses another type of conventional
image display apparatus. In the conventional image display
apparatus, as shown in FIG. 22, an image of an image display device
is transferred to a curved object surface by an image transfer
device, and the image transferred to the object surface is
projected in the air by a toric reflector.
U.S. Reissued Pat. No. 27,356 discloses another type of
conventional image display apparatus. As shown in FIG. 23, the
apparatus is an ocular optical system designed to project an object
surface on an exit pupil by a semitransparent concave mirror and a
semitransparent plane mirror.
However, an image display apparatus of the type in which an image
of an image display device is relayed, as in the image display
apparatus shown in FIG. 20, must use several lenses as a relay
optical system in addition to an ocular optical system, regardless
of the type of ocular optical system .Consequently, the optical
path length increases, and the optical system increases in both
size and weight.
In a layout such as that shown in FIGS. 21(a) and 21(b), the amount
to which the apparatus projects from the observer's face
undesirably increases. Further, since an image display device and
an illumination optical system are attached to the projecting
portion of the apparatus, the apparatus becomes increasingly large
in size and heavy in weight.
Since a head-mounted image display apparatus is fitted to the human
body, particularly the head, if the amount to which the apparatus
projects from the user's face is large, the distance from the
supporting point on the head to the center of gravity of the
apparatus is long. Consequently, the weight of the apparatus is
imbalanced when the apparatus is fitted to the observer's head.
Further, when the observer moves or turns with the apparatus fitted
to his/her head, the apparatus may collide with something.
That is, it is important for a head-mounted image display apparatus
to be small in size and light in weight An essential factor in
determining the size and weight of the apparatus is the layout of
the optical system.
However, if an ordinary magnifier alone is used as an ocular
optical system, exceedingly large aberrations are produced, and
there is no device for correcting them. Even if spherical
aberration can be corrected to a certain extent by forming the
configuration of the concave surface of the magnifier into an
aspherical surface, other aberrations such as coma and field
curvature remain. Therefore, if the field angle for observation is
increased, the image display apparatus becomes impractical.
Alternatively, if a concave mirror alone is used as an ocular
optical system it is necessary to use not only ordinary optical
elements (lens and mirror) but also a device for correcting field
curvature by an image transfer device (fiber plate) having a
surface which is curved in conformity to the field curvature
produced, as shown in FIG. 22.
In a coaxial ocular optical system in which an object surface is
projected on an observer's pupil by using a semitransparent concave
mirror and a semitransparent plane mirror, as shown in FIG. 23,
since two semitransparent surfaces are used, the brightness of the
image is reduced to as low a level as 1/16, even in the case of a
theoretical value. Further, since field curvature that is produced
by the semi-transparent concave mirror is corrected by curving the
object surface itself, it is difficult to use a flat display, e.g.
an LCD (Liquid Crystal Display), as an image display device.
SUMMARY OF THE INVENTION
In view of the above-described problems of the conventional
techniques, an object of the present invention is to provide an
image display apparatus which enables observation of a clear image
at a wide field angle with substantially no reduction in the
brightness of the observation image, and which is extremely small
in size and light in weight and hence unlikely to cause the
observer to be fatigued.
To attain the above-described object, the present invention
provides a first image display apparatus which includes an image
display device for displaying an image, and an ocular optical
system for projecting the image formed by the image display device
and for leading the projected image to an observer's eyeball. The
ocular optical system is arranged such that light rays emitted from
the image display device are reflected three or higher odd-numbered
times before reaching the observer's eyeball, and that a surface of
the ocular optical system that is disposed immediately in front of
the observer's eyeball is a refracting surface which internally
reflects the light rays, and through which the light rays exit from
the ocular optical system.
In addition, the present invention provides a second image display
apparatus which includes an image display device for displaying an
image, and an ocular optical system for projecting the image formed
by the image display device and for leading the projected image to
an observer's eyeball. The ocular optical system is arranged such
that light rays emitted from the image display device are reflected
three times before reaching the observer's eyeball, and that a
surface of the ocular optical system that is disposed immediately
in front of the observer's eyeball is a refracting surface which
internally reflects the light rays, and through which the light
rays exit from the ocular optical system.
In addition, the present invention provides a third image display
apparatus which includes an image display device for displaying an
image, and an ocular optical system for projecting the image formed
by the image display device and for leading the projected image to
an observer's eyeball.
The ocular optical system has at least three surfaces, and a space
formed by the at least three surfaces is filled with a medium
having a refractive index larger than 1. The at least three
surfaces include, in the order in which light rays pass in backward
ray tracing from the observer's eyeball to the image display
device, a first surface which functions as both a refracting
surface and an internally reflecting surface, a second surface
which is a reflecting surface facing the first surface and
decentered or tilted with respect to an observer's visual axis, and
a third surface which is a refracting surface closest to the image
display device, so that reflection takes place three times in the
path from the observer's eyeball to the image display device.
In addition, the present invention provides a fourth image display
apparatus which includes an image display device for displaying an
image, and an ocular optical system for projecting the image formed
by the image display device and for leading the projected image to
an observer's eyeball. The ocular optical system has at least four
surfaces, and a space formed by the at least four surfaces is
filled with a medium having a refractive index larger than 1. The
at least four surfaces include, in the order in which light rays
pass in backward ray tracing from the observer's eyeball to the
image display device, a first surface which functions as both a
refracting surface and an internally reflecting surface, a second
surface which is a reflecting surface facing the first surface and
decentered or tilted with respect to an observer's visual axis, a
third surface which is a reflecting surface facing the first
surface and adjacent to the second surface, and a fourth surface
which is a refracting surface closest to the image display device,
so that reflection takes place three times in the path from the
observer's eyeball, to the image display device.
The reasons for adopting the above-described arrangements in the
present invention, together with the functions and effects thereof,
will be explained below. The following explanation will be made on
the basis of backward ray tracing in which light rays are traced
from the observer's pupil position toward the image display device
for the convenience of designing the optical system.
In the first image display apparatus according to the present
invention, the ocular optical system is characterized in that light
rays emitted from the image display device are reflected three or
higher odd-numbered times before reaching the observer's eyeball,
and that a surface of the ocular optical system that is disposed
immediately in front of the observer's eyeball is a refracting
surface which internally reflects the light rays, and through which
the fight rays exit from the ocular optical system. Examples 1 to
10 (described later) correspond to the arrangement of the first
image display apparatus.
In this apparatus, light rays emitted from the image display device
are reflected at least three times in the ocular optical system,
thereby enabling the light rays to be folded very effectively and
favorably, and thus succeeding in minimizing the thickness of the
ocular optical system and realizing reduction in both size and
weight of the image display apparatus. In addition, because light
rays emitted from the image display device are reflected an odd
number of times, the image display device can be installed in such
a manner that a side thereof which is reverse to its display
surface faces the observer. Further, in the case of an image
display device which is illuminated from behind it, e.g. an LCD
(Liquid Crystal Display), a back light and other attachments are
disposed behind the image display device. In this regard, the
present invention enables these attachments to be disposed along
the observer's face. Accordingly, no part of the image display
device projects forwardly beyond the ocular optical system In other
words, the whole image display apparatus can be arranged such that
the amount to which the optical system projects from the observer's
face is extremely small. Thus, a compact and lightweight
head-mounted image display apparatus can be realized.
Further, a surface of the ocular optical system that is disposed
immediately in front of the observer's face is adapted to perform
both refraction and reflection. Therefore, it is possible to reduce
the number of surfaces needed to constitute the ocular optical
system and hence possible to improve productivity. In addition, if
the angle of internal reflection at the first surface is set so as
to be larger than the critical angle, it becomes unnecessary to
provide the first surface with a reflective coating. Therefore,
even if the transmitting and reflecting regions on the first
surface overlap each other, the image of the image display device
reaches the observer's eyeball without any problem. Accordingly,
the ocular optical system can be arranged in a compact form, and
the field angle for observation can be widened.
In the second image display apparatus according to the present
invention, the ocular optical system is characterized in that light
rays emitted from the image display device are reflected three
times before reaching the observer's eyeball, and that a surface of
the ocular optical system that is disposed immediately in front of
the observer's eyeball is a refracting surface which internally
reflects the light rays, and through which the light rays exit from
the ocular optical system Examples 1 to 10 (described later)
correspond to the arrangement of the second image display
apparatus.
In this apparatus, light rays emitted from the image display device
are reflected three times in the ocular optical system, thereby
enabling the light rays to be folded very effectively and
favorably, and thus succeeding in minimizing the thickness of the
ocular optical system and realizing reduction in both size and
weight of the image display apparatus. Light rays emanating from
the observer's pupil is first reflected toward the observer's face.
Then, by the second reflection, the light rays are reflected
forwardly from the observer's face side. By the third reflection,
the light rays are reflected toward the observer's face again to
reach the image display device. Therefore, the image display device
lies closer to the observer, and the image display device can be
disposed in such a manner that a side thereof which is reverse to
its display surface faces the observer. Accordingly, it is possible
to realize a head-mounted image display apparatus which projects
from the observer's face to an extremely small amount for the same
reasons as set forth above with respect to the second image display
apparatus according to the present invention. Although it is
possible to obtain similar advantageous effects by arranging the
ocular optical system such that the fight rays are reflected five
or higher odd-numbered times, an increase in the number of
reflections causes the distance from the image display device to
the observer's pupil position to lengthen exceedingly.
Consequently, it becomes necessary to use longer and larger optical
elements. Further, it becomes difficult to ensure a wide field
angle because the focal length of the ocular optical system becomes
long. Accordingly, the use of the ocular optical system which
allows the image of the image display device to reach the
observer's eyeball by three reflections makes it possible to
realize a well-balanced image display apparatus.
Further, a surface of the ocular optical system that is disposed
immediately in front of the observer's face is adapted to perform
both refraction and reflection. Therefore, it is possible to reduce
the number of surfaces needed to form the ocular optical system and
hence possible to improve productivity. In addition, if the angle
of internal reflection at the first surface is set so as to be
larger than the critical angle, it becomes unnecessary to provide
the first surface with a reflective coating. Therefore, even if the
transmitting and reflecting regions on the first surface overlap
each other, the image of the image display device reaches the
observer's eyeball without any problem. Accordingly, the ocular
optical system can be arranged in a compact form, and the field
angle for observation can be widened.
In the third image display apparatus according to the present
invention, the ocular optical system has at least three surfaces,
and a space formed by the at least three surfaces is filled with a
medium having a refractive index larger than 1. The at least three
surfaces include, in the order in which light rays pass in backward
ray tracing from the observer's eyeball to the image display
device, a first surface which functions as both a refracting
surface and an internally reflecting surface, a second surface
which is a reflecting surface facing the first surface and
decentered or tilted with respect to an observer's visual axis, and
a third surface which is a refracting surface closest to the image
display device, so that reflection takes place three times in the
path from the observer's eyeball to the image display device.
Examples 1 to 5 (described later) correspond to the arrangement of
the third image display apparatus.
In this apparatus, a space that is formed by the first, second and
third surfaces of the ocular optical system is filled with a medium
having a refractive index larger than 1, and light rays emitted
from the image display device are reflected three times in the
ocular optical system, thereby enabling the light rays to be folded
very effectively and favorably, and thus succeeding in minimizing
the thickness of the ocular optical system realizing reduction in
both size and weight of the image display apparatus, and providing
the observer with a clear observation image having a wide exit
pupil diameter and a wide field angle.
By filling the space formed by the first, second and third surfaces
with a medium having a refractive index larger than 1, light rays
from the pupil are refracted by the first surface, and it is
therefore possible to minimize the height at which extra-axial
principal and subordinate rays are incident on the second surface.
Consequently, the height of the principal ray at the second surface
is low, and therefore, the size of the second surface is minimized.
Thus, the ocular optical system can be formed in a compact
structure. Alternatively, the field angle can be widened. Further,
because the height of the subordinate rays is reduced, it is
possible to minimize comatic aberrations produced by the second
surface, particularly higher-order comatic aberrations.
Further, the actual optical path length is equal to the product of
the apparent optical path length multiplied by the refractive index
(e.g. 1.5) of the medium. Therefore, it become easy to ensure the
distance from the observer's eyeball to the ocular optical system,
or the distance from the ocular optical system to the image display
device.
Further, unlike a conventional arrangement in which an observation
image of an image display device is formed in the air as a real
intermediate image by a relay optical system and projected into an
eyeball as an enlarged image by an ocular optical system the image
display apparatus according to the present invention is arranged to
project the image of the image display device directly into an
observer's eyeball as an enlarged image, thereby enabling the
observer to see the enlarged image of the image display device as a
virtual image. Accordingly, the optical system can be formed from a
relatively small number of optical elements. Further, because the
second surface of the ocular optical system, which is a reflecting
surface, can be disposed immediately in front of the observer's
face in a configuration conformable to the curve of his/her face,
the amount to which the optical system projects from the observer's
face can be reduced to an extremely small value. Thus, a compact
and lightweight image display apparatus can be realized.
Further, because the ocular optical system comprises as small a
number of surfaces as three, the mechanical design is facilitated,
and the arrangement of the optical system is superior in
productivity in the process of machining optical elements. Thus it
is possible to realize an optical system of low cost and high
productivity.
In the fourth image display apparatus, the ocular optical system
has at least four surfaces, and a space formed by the at least four
surfaces is filled with a medium having a refractive index larger
than 1. The at least four surfaces include, in the order in which
light rays pass in backward ray tracing from the observer's eyeball
to the image display device, a first surface which functions as
both a refracting surface and an internally reflecting surface, a
second surface which is a reflecting surface facing the first
surface and decentered or tilted with respect to an observer's
visual axis, a third surface which is a reflecting surface facing
the first surface and adjacent to the second surface, and a fourth
surface which is a refracting surface closest to the image display
device, so that reflection takes place three times in the path from
the observer's eyeball to the image display device. Examples 6 to
10 (described later) correspond to the arrangement of the fourth
image display apparatus.
In this apparatus, light rays emitted from the image display device
are reflected three times in the ocular optical system in the same
way as in the third image display apparatus, thereby enabling the
light rays to be folded very effectively and favorably, and thus
succeeding in minimizing the thickness of the ocular optical system
realizing reduction in both size and weight of the image display
apparatus, and providing the observer with a clear observation
image having a wide exit pupil diameter and a wide field angle.
In the fourth image display apparatus, because the ocular optical
system comprises four surfaces, only the first surface performs
both transmission and reflection, and other reflecting and
refracting functions are performed by respective surfaces which are
independent of each other. Accordingly, these surfaces can correct
each other's aberrations, and hence the arrangement is remarkably
useful for aberration correction.
In a case where, as shown in FIG. 6, the image display device 4
.Iadd.(image plane) .Iaddend.is disposed above the observer's face
or at a side of the observer's face, the image display device 4
.Iadd.(image plane) .Iaddend.is disposed obliquely in front of the
fourth surface 14, which is in close proximity to the image display
device 4 .Iadd.(image plane).Iaddend., thereby enabling the whole
apparatus to be arranged in a structure which is compact and will
not interfere with the observer's face. In the image display
apparatus according to the present invention in which the ocular
optical system comprises three surfaces, light rays are reflected
twice by the second surface. Accordingly, if the radius of
curvature of the second surface is reduced, the image display
device is likely to be disposed closer to the observer's face. When
an LCD is used as an image display device in particular, a back
light, driving substrate, etc. undesirably project. Therefore, the
apparatus is likely to interfere with the observer's face. If the
radius of curvature of the second surface is increased, the
distance between two points on the second surface at which two
reflections take place, respectively, increases, and hence the
second surface increases in length. Consequently, the first surface
also increases in length, causing the optical system itself to
increase in size unfavorably.
In contrast, the ocular optical system which comprises four
surfaces is free from the above-described problem. That is, in the
fourth image display apparatus, the function of the second surface
in the triple surface structure is divided between the second and
fourth surfaces. Accordingly, there are two surfaces which are
disposed opposite to the observer's face to reflect light rays
toward the observer. Therefore, it is possible to reflect an
optical path by each of the second and fourth surfaces in a
favorable direction without depending on the curvature of each
surface. In other words, it is possible to arrange the optical
system in a compact form and set the apparatus in a favorable
direction without causing the image display device 4 .Iadd.(image
plane) .Iaddend.to interfere with the observer's face.
In the above-described image display apparatuses, at least one of
the surfaces constituting the ocular optical system may be a flat
surface. Examples 5 and 6 (described later) correspond to this
arrangement.
That is, if at least one surface of the ocular optical system is a
flat surface, the other surfaces can be defined with the flat
surface used as a reference; this facilitates the mechanical design
and production of the ocular optical system. Thus, it also becomes
possible to shorten the machining time and readily arrange the
layout of the whole apparatus. Accordingly, it is possible to
realize a considerable cost reduction.
In the third and fourth image display apparatuses, it is desirable
that the internal reflection at the first surface should be total
reflection. Examples, 1, 2, 3, 6, 7 and 8 (described later)
correspond to this arrangement.
That is, if the light rays reflected by the second surface are
totally reflected by the first surface, it is possible to obtain
great advantages in terms of the size of the optical elements and
from the viewpoint of performance. This will be explained below in
detail.
FIGS. 14(a) and 14(b) are sectional views each illustrating an
optical ray trace of the image display apparatus according to the
present invention. FIG. 14(a) shows an ocular optical system in
which a first surface 5 does not totally reflect light rays. FIG.
14(b) shows an ocular optical system in which total reflection
occurs at a first surface 5. In these sectional views, reference
numeral 1 denotes an observer's pupil position, 2 an observer's
visual axis, 3 an ocular optical system, 4 an image display device
.Iadd.(image plane).Iaddend., 5 a first surface of the ocular
optical system 3, 6 a second surface of the ocular optical system
3, and 7 a third surface of the ocular optical system 3. In FIG.
14(a), an internally reflecting region M of the first surface 5 has
been mirror-coated. The other region of the first surface 5 is a
refracting region.
Light rays coming out of the pupil 1 are refracted by the first
surface 5 of the ocular optical system 3, reflected by the second
surface 6, which is a concave mirror, and internally reflected by
the first surface 5. If, as shown in FIG. 14(a), there is a large
difference between the height at which upper extra-axial light rays
U are reflected by the second surface 6 and the height at which the
upper extra-axial light rays U are reflected by the first surface 5
after being reflected by the second surface 6, the overall length
of the ocular optical system 3 correspondingly increases, resulting
in an increase of the overall size of the ocular optical system 3.
That is, as the difference between the heights of the reflection
points decreases, the size of the ocular optical system 3 can be
made smaller In other words, if the size of the ocular optical
system is kept constant, as the difference between the heights of
the reflection points becomes smaller, the field angle for
observation can be widened.
However, if the difference between the reflection heights of the
upper extra-axial light rays U at the second surface 6 and the
first surface 5 is reduced in the ocular optical system of the
present invention, as shown in FIG. 14(b), the upper light rays U
are reflected at a position higher than a position at which lower
extra-axial light rays L are incident on the first surface 5.
Accordingly, when the first surface 5 is not a totally reflecting
surface, the refracting region of the first surface 5 overlaps the
mirror coat region M'. Consequently, the lower light rays L are
undesirably blocked.
That is, if the internal reflection at the first surface 5
satisfies the condition for total reflection, the first surface 5
need not be mirror-coated. Therefore, even if the upper light rays
U after reflection at the second surface 6 and the lower light rays
L incident on the first surface 5 interfere with each other at the
first surface 5, the upper and lower light rays U and L can perform
their original functions. At the second surface 6, which is a
decentered reflecting surface, as the reflection angle becomes
larger, comatic aberration occurs to a larger extent. However, in a
case where light rays are totally reflected by the first surface 5,
the angle of reflection at the second surface 6 can be reduced.
Therefore, it is possible to effectively suppress the occurrence of
comatic aberration at the second surface 6.
It should be noted that the above-described effect does not depend
on the number of surfaces constituting the ocular optical
system.
Further, it is desirable that the second surface should be arranged
as a reflecting surface which is concave toward the first surface.
Examples, 1, 2, 3, 4, 6, 7 and 8 (described later) correspond to
this arrangement.
In a case where the second surface is a reflecting surface which is
concave toward the first surface, the second surface is a principal
reflecting surface having a positive power in the ocular optical
system. Principal rays diverging from the pupil at a certain angle
(field angle) are reflected by the second surface having a positive
power, thereby enabling the angle to be reduced. Accordingly, it is
possible to reduce the size of all the surfaces, from the first to
third surfaces after the reflection at the second surface, and
hence possible to arrange the whole optical system in a compact and
lightweight structure.
Generally, a concave mirror which is decentered with respect to an
optical axis causes axial and off-axis comatic aberrations to be
produced by decentration. Further, as the power of a surface
increases, the amount of aberration produced by the surface also
increases. However, in the ocular optical system according to the
present invention, light rays are reflected twice by the second
surface. Therefore, it is possible to obtain an adequate positive
power for the whole system without the need to increase the power
of the second surface. Accordingly, it is possible to minimize the
amount of aberration produced by each reflection at the second
surface.
Further, it is desirable that the first surface should be a surface
which functions as both a transmitting surface and a reflecting
surface, and which is convex toward the second surface. Examples 1,
2, 3, 4, 7 and 8 (described later) correspond to this
arrangement.
In a case where the first surface functions as both a transmitting
surface and a reflecting surface and is convex toward the second
surface, and the second surface has a positive power, it is
possible to effectively correct coma and field curvature produced
by the second surface when light rays are internally reflected by
the first surface after being reflected by the second surface.
In a case where the second surface is a reflecting surface having a
positive power, the negative comatic aberration produced by the
second surface can be corrected by allowing the first surface to
have a negative power so that the first surface produces comatic
aberration which is opposite in sign to the comatic aberration
produced by the second surface. The positive field curvature
produced by the second surface can be simultaneously corrected by
producing negative field curvature at the first surface.
In order to allow the first surface to perform total reflection as
internal reflection, it is necessary to satisfy the condition that
reflection angles of all light rays at the first surface are not
smaller than the critical angle .theta..sub.r =sin.sup.-1 (1/n)
(where n is the refractive index of a medium constituting the
optical system). In the case of n=1.5, for example, .theta..sub.r
=41.81.degree., and a reflection angle not smaller than it is
necessary. This will be explained below with reference to FIGS.
15(a) and 15(b). FIGS. 15(a) and 15(b) show a part of the ocular
optical system in which light rays are first reflected by the
second surface 6 and then internally reflected by the first surface
5. FIG. 15(a) shows the way in which reflection takes place when
the first surface 5 is concave toward the second surface 6. FIG.
15(b) shows the way in which reflection takes place when the first
surface 5 is convex toward the second surface 6.
After being reflected by the second surface 6, each light ray is
directed downward at a certain reflection angle. In a case where
the first surface 5 is a reflecting surface which is concave toward
the second surface 6. As shown in FIG. 15(a), lines S normal to the
first surface 5 convergently extend toward the second surface 6.
Since a lower light ray L reflected by the second surface 6 is
incident on the first surface 5 in a direction along the line
normal to the first surface 5, the reflection angle .gamma. at the
first surface 5 cannot be made large. That is, it is difficult to
satisfy the condition for total reflection with respect to all
fight rays reflected by the first surface 5. Conversely, in a case
where the first surface 5 is convex toward the second surface 6, as
shown in FIG. 15(b), lines S' normal to the first surface 5
divergently extend toward the second surface 6. Accordingly, the
reflection angle .gamma. can be effectively increased even for the
lower light ray. Thus, the condition for total reflection at the
first surface 5 can be readily satisfied at a wide field angle.
Further, the first surface may be a flat surface which functions as
both a transmitting surface and a reflecting surface. Example 6
(described later) corresponds to this arrangement.
If the first surface is a flat surface, the other surfaces can be
defined with the flat surface used as a reference; this facilities
the mechanical design and production of the ocular optical system.
Thus, it also becomes possible to shorten the machining time and
readily arrange the layout of the whole apparatus. Accordingly, it
is possible to realize a considerable cost reduction. Further, when
an outside world image is to be observed through the ocular optical
system, it is necessary to arrange the system such that a
compensating optical system for viewing the outside world is
disposed outside the second surface so that the power of the entire
optical system is approximately zero with respect to light from the
outside world. In such a case, if the first surface is a flat
surface, both the entrance and exit surfaces of the optical system
are flat surfaces. Therefore, even if the first surface is tilted,
the outside world can be readily observed. If the compensating
optical system is cemented to the second surface, the resulting
structure is a simple plane-parallel plate with respect to the
outside world light and hence completely powerless. That is, the
magnification is 1. Thus, the outside world can be observed in a
natural state.
Further, the internally reflecting region of the first surface may
be provided with a reflective coating. Examples 4, 5, 9 and 10
(described later) correspond to this arrangement.
When the internal reflection at the first surface does not satisfy
the condition for total reflection, the internally reflecting
region of the first surface needs to be provided with a reflective
coating of aluminum, for example.
Further, the first surface may be a surface which functions as both
a transmitting surface and a reflecting surface, and which is
concave toward the second surface. Examples 5, 9 and 10 (described
later) correspond to this arrangement.
In a case where the first surface has a positive power, light rays
are refracted by the first surface even more effectively.
Therefore, it is possible to further reduce the height at which
light rays are incident on the second surface. This action makes it
possible to reduce the amount of comatic aberration produced by
decentration at the second and later reflecting surfaces.
Further, the second surface may be a reflecting surface which is
convex toward the first surface. Examples 9 and 10 (described
later) correspond to this arrangement.
In a case where the first surface has a positive power, the second
surface must have a negative power in order to ensure an optical
path length required for the optical system. In the case of an
ocular optical system having a wide field angle as in the present
invention, the optical system can be arranged in a compact
structure by placing a positive power at a position close to the
exit pupil. However, the first surface not only refracts but also
reflects light rays after they have been reflected by the second
surface. With respect to surfaces of the same curvature, reflective
power is stronger than refractive power. In other words, the focal
length becomes exceedingly short. Therefore, an appropriate focal
length is obtained by giving a negative power to the second
surface, thus enabling the image display device to be readily
disposed at a predetermined position.
Further, it is desirable to satisfy the following condition:
where .theta..sub.2 is the incident angle of the axial principal
ray at the first reflection by the second surface in the backward
ray tracing.
Examples 1 to 10 (described later) correspond to this
arrangement.
FIG. 16 shows the way in which, in the ocular optical system 3 in
the image display apparatus according to the present invention, an
axial principal ray, which exits from the center of the pupil 1 and
reaches the center of the image display device 4 .Iadd.(image
plane).Iaddend., emits from the image display device 4 .Iadd.(image
plane) .Iaddend.and reaches the observer's pupil 1, together with
incident angles .theta..sub.1 to .theta..sub.5 set at the surfaces
4 to 7 and .theta..sub.i. The sign of each angle is positive when
the angle is determined in the direction illustrated in FIG. 16
from the perpendicular S at the reflection point.
The above expression (1) is a condition for disposing the ocular
optical system and the image display device in the image display
apparatus according to the present invention at appropriate
positions, respectively. If the incident angle .theta..sub.2 is not
larger than the lower limit of the condition (1), i.e. 0.degree.
light rays reflected by the second surface undesirably return to
the observer, making it impossible to perform observation.
Conversely, if the incident angle .theta..sub.2 is not smaller than
the upper limit, i.e. 50.degree., the distance to the reflection
point on the first surface increases, causing the second surface to
lengthen. Consequently, the optical system becomes undesirably
large in size.
Further, it is preferable to satisfy the following condition:
where .theta..sub.2 is the incident angle of the axial principal
ray at the first reflection by the second surface in the backward
ray tracing.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (2) is a condition for disposing the ocular
optical system and the image display device in the image display
apparatus according to the present invention at appropriate
positions, respectively. If the incident angle .theta..sub.2 is not
larger than the lower limit of the condition (2), i.e. 10.degree.,
the angle of incidence on the first surface of the light rays
reflected from the second surface cannot satisfy the condition for
the critical angle in a case where the light rays are totally
reflected by the second surface. As a result, the light rays
undesirably return to the observer through the optical system,
making it impossible to perform observation. Conversely, if
.theta..sub.2 is not smaller than the upper limit, i.e. 40.degree.,
the reflection angle becomes undesirably large, causing comatic
aberration to be produced by decentration to such an extent that it
cannot satisfactorily be corrected by another surface.
Consequently, it becomes difficult to observe a sharp image.
Further, it is desirable to satisfy the following condition:
where .theta..sub.1 is the incident angle of the axial principal
ray at the first surface.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (3) is a condition for disposing the ocular
optical system in the image display apparatus according to the
present invention at an appropriate position or at an appropriate
angle. If the .theta..sub.1 is not larger than the lower limit of
the condition (3), i.e. -20.degree., the ocular optical system
undesirably bows toward the observer. Therefore, the apparatus is
likely to interfere with the observer's head. Conversely, if
.theta..sub.1 is not smaller than the upper limit, i.e. 40.degree.,
the ocular optical system undesirably projects forwardly, resulting
in an apparatus of body weight balance.
Further, it is preferable to satisfy the following condition:
where .theta..sub.1 is the incident angle of the axial principal
ray at the first surface.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (4) is a condition for disposing the ocular
optical system in the image display apparatus according to the
present invention at an appropriate position or at an appropriate
angle. If the .theta..sub.1 is not larger than the lower limit of
the condition (4), i.e. -10.degree., the ocular optical system
undesirably bows toward the observer. Therefore, the apparatus is
likely to interfere with the observer's head. Conversely, if
.theta..sub.1 is am smaller than the upper limit i.e. 25.degree.,
the amount of chromatic aberrations produced by the first surface
increases. Particularly, off-axis lateral chromatic aberration
markedly appears, making it difficult to observe a sharp image.
Further, it is desirable to satisfy the following condition:
where .theta..sub.3 is the incident angle of the axial principal
ray at the internal reflection by the first surface.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (5) is a condition for arranging the ocular
optical system in the image display apparatus according to the
present invention in a structure which is compact and lightweight
and yet enables observation. If .theta..sub.3 is not larger than
the lower limit of the condition (5), i.e. 20.degree., the light
rays internally reflected by the first surface return to the second
surface and are then reflected by the first surface to return to
the observer's face, making it impossible to perform observation.
If .theta..sub.3 is not smaller than the upper limit, i.e.
70.degree., a position at which light rays reach the second or
third (in the case of the ocular optical system comprising four
surfaces) after being reflected by the first surface is undesirably
far away from the reflection point. Consequently, the optical
system undesirably increases in size.
Further, it is preferable to satisfy the following condition:
where .theta..sub.3 is the incident angle of the axial principal
ray at the internal reflection by the first surface.
Examples 1 to 10 (described later) correspond to this arrangement
The above expression (6) is a condition for arranging the ocular
optical system in the image display apparatus according to the
present invention in a structure which is compact and lightweight
and yet enables observation. If .theta..sub.3 is not larger than
the lower Emit of the condition (6), i.e. 30.degree., it becomes
difficult to satisfy the condition for the critical angle at the
first surface, and it becomes impossible to perform observation.
Conversely, if .theta..sub.3 is not smaller than the upper Emit,
i.e. 55.degree., a position at which light rays reach the second or
third (in the case of the ocular optical system comprising four
surfaces) after being reflected by the first surface is undesirably
far away from the reflection point, Consequently, the optical
system undesirably increases in size.
Further, it is desirable to satisfy the following condition:
where .theta..sub.4 is the incident angle of the axial principal
ray when reflected for a second time in the backward ray tracing by
the second surface of the ocular optical system comprising three
surfaces, or .theta..sub.4 is the incident angle of the axial
principal ray at the third surface of the ocular optical system
comprising four surfaces.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (7) is a condition for enabling the observer
to view the image of the image display device clearly over the
length and breadth of it through the ocular optical system of the
image display apparatus according to the present invention. If
.theta..sub.4 is not larger than the lower limit of the condition
(7), i.e. 20.degree., light rays undesirably return to the first
surface. Therefore, the reflected light rays undesirably reach the
observer's face, making it impossible to perform observation.
Conversely, if .theta..sub.4 is not smaller than the upper limit,
i.e. 80.degree., the distance from the internal reflection point on
the first surface becomes exceedingly long, causing the optical
system to lengthen downward as viewed in FIG. 16. As a result, the
optical system becomes undesirably large in size.
Further, it is preferable to satisfy the following condition:
where .theta..sub.4 is the incident angle of the axial principal
ray when reflected for a second time in the backward ray tracing by
the second surface of the ocular optical system comprising three
surfaces, or .theta..sub.4 is the incident angle of the axial
principal ray at the third surface of the ocular optical system
comprising four surfaces.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (8) is a condition for enabling the observer
to view the image of the image display device clearly over the
length and breadth of it through the ocular optical system of the
image display apparatus according to the present invention. If
.theta..sub.4 is not larger than the lower limit of the condition
(9), i.e. 30.degree., light rays are reflected in a direction
closer to the pupil direction (i.e. in an upward direction as
viewed in FIG. 16), causing extra-axial light rays to interfere
with the first surface when the reflected light rays reach the
third surface or the fourth surface (in the case of the ocular
optical system comprising four surfaces). Thus, it becomes
difficult to observe the image clearly over the length and breadth
of it Conversely, if .theta..sub.4 is not smaller than the upper
limit, i.e. 65.degree., the angle of reflection at the second or
third surface becomes excessively large, causing comatic aberration
to be produced by decentration to such an extent that it cannot
satisfactorily be corrected by another surface. Consequently, it
becomes difficult to observe a sharp image.
Further, it is desirable to satisfy the following condition:
where .theta..sub.5 is the incident angle of the axial principal
ray at the third surface in the ocular optical system comprising
three surfaces, or .theta..sub.5 is the incident angle of the axial
principal ray at the fourth surface in the ocular optical system
comprising four surfaces.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (9) is a condition for disposing the ocular
optical system and the image display device in the image display
apparatus according to the present invention at appropriate
positions, respectively. If .theta..sub.5 is not larger than the
lower limit of the condition (9), i.e. -30.degree., light rays are
refracted in a direction away from the pupil direction (i.e. in a
downward direction as viewed in FIG. 16), causing the image display
device to come away from the pupil. Consequently, the overall size
of the apparatus increases undesirably. Conversely, if
.theta..sub.5 is not smaller than the upper limit, i.e. 40.degree.,
light rays are reflected in a direction closer to the pupil
direction (i.e. in an upward direction as viewed in FIG. 16).
Consequently, the image display device is disposed closer to the
observer's face. Thus, it becomes likely that the image display
device will interfere with the observer's face.
Further, it is desirable to satisfy the following condition:
where .theta..sub.i is the incident angle of the axial principal
ray at the display surface of the image display device.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (10) is a condition for enabling the observer
to view the image of the image display device clearly over the
length and breadth of it through the ocular optical system of the
image display apparatus according to the present invention. If
.theta..sub.i is not larger than the lower limit of the condition
(10), i.e. -40.degree., or not smaller, than the upper limit of the
condition (10), i.e. 40.degree., light emitted from the image
display device cannot sufficiently be supplied to the observer's
pupil. Hence, it becomes difficult to observe a bright and clear
image.
Further, it is preferable to satisfy the following condition:
where .theta..sub.i is the incident angle of the axial principal
ray at the display surface of the image display device.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (11) is a condition for enabling the observer
to view the image of the image display device. clearly over the
length and breadth of it through the ocular optical system of the
image display apparatus according to the present invention. If
.theta..sub.i is not larger than the lower limit of the condition
(11), i.e. -25.degree., or not smaller than the upper limit of the
condition (11), i.e. 25.degree., the image for observation has an
undesirably low contrast in a case where the image display device
has a small viewing angle as viewing angle characteristic.
Particularly, in the case of an LCD (Liquid Crystal Display),
reversal of the image is likely to occur because of the small
viewing angle, making it difficult to observe the image
clearly.
Further, it is desirable to satisfy the following condition:
where N.sub.d is the refractive index for the spectral d-line of
the medium having a refractive index larger than 1.
Examples 1 to 10 (described later) correspond to this
arrangement.
The above expression (12) is a condition concerning the refractive
index of the medium that fills the space formed by the at least
three surfaces. It is desirable that the ocular optical system of
the image display apparatus according to the present invention
should be formed by using a transparent medium of high transparency
which is known as "optical glass" or "optical plastic". In this
case, the refractive index for the spectral d-line of the medium
must satisfy the condition (12). If the refractive index N.sub.d is
not larger than the lower limit of the condition (12) or not
smaller than the upper limit of the condition (12), transparency
becomes undesirably low, and machinability degrades.
Further, it is preferable to satisfy the following condition:
where N.sub.d Nd is the refractive index for the spectral d-line of
the medium having it refractive index larger than 1.
Examples 1 to 5 and 7 to 10 (described later) correspond to this
arrangement.
It is favorable for the ocular optical system of the image display
apparatus according to the present invention to have as large a
refractive index as possible in order to satisfy the condition for
internal reflection at the first surface. Therefore, it is
desirable to use a medium that satisfies the condition (13). If the
refractive index N.sub.d is not larger than the lower limit of the
condition (13), i.e. 1.5, extra-axial light rays cannot satisfy the
condition for total reflection at the first surface, particularly
in the cue of a wide field angle. Therefore, there are cases where
it is difficult to observe the edge of the image.
Further, it is desirable that at least one of the surfaces
constituting the ocular optical system should be an aspherical
surface.
Examples 1 to 10 (described later) correspond to this
arrangement.
It is effective for aberration correction that any one of the
first, second and third surfaces of the ocular optical system is an
aspherical surface. This is an important condition for correcting
comatic aberrations, particularly higher-order comatic aberrations
and coma flare, produced by the second surface 6 (see FIG. 1),
which is decentered in a direction Y or tilted with respect to the
visual axis 2 in a coordinate system (described later) which is
defined as follows: As shown in FIG. 1, with the observer's iris
position 1 defined as the origin, the direction of an observer's
visual axis 2 is taken as the Z-axis, where the direction toward an
ocular optical system 3 from the origin is defined as the positive
direction, and the vertical direction (as viewed from the
observer's eyeball) which perpendicularly intersects the observer's
visual axis 2 is taken as the Y-axis, where the upward direction is
defined as positive direction. Further, the horizontal direction
(as viewed from the observer's eyeball) which perpendicularly
intersects the observer's visual axis 2 is taken as the X-axis,
where the leftward direction is defined as the positive
direction.
In an image display apparatus which uses an ocular optical system
of the type having a decentered or tilted reflecting surface in
front of an observer's eyeball as in the present invention, light
rays are obliquely incident on the reflecting surface, even on the
axis. Therefore, complicated comatic aberration is produced at the
center axis of the reflecting mirror. The complicated comatic
aberration increases as the inclination angle of the reflecting
surface becomes larger. However, if it is intended to realize a
compact and wide-field image display apparatus, it is difficult to
ensure an observation image having a wide field angle unless the
amount of eccentricity (decentration) or the angle of inclination
is increased to a certain extent because of the interference
between the image display device and the optical path. Accordingly,
as the field angle of an image display apparatus becomes wider and
the size thereof becomes smaller, the inclination angle of the
reflecting surface becomes larger. As a result, how to correct
comatic aberration due to decentration becomes a serious
problem
To correct such complicated comatic aberration, any one of the
first, second and third surfaces constituting the ocular optical
system is formed into a decentered aspherical surface. By doing so,
the power of the optical system can be made asymmetric with respect
to the visual axis. Further, the effect of the aspherical surface
can be utilized for off-axis aberration. Accordingly, it becomes
possible to effectively correct comatic aberrations, including
axial aberration.
Further, it is desirable that any one of the surfaces constituting
the ocular optical system should be an anamorphic surface.
Examples 1 to 10 (described later) correspond to this
arrangement.
It is desirable that any one of the first, second and third
surfaces of the ocular optical system should be an anamorphic
surface. That is, any one of the three surfaces should be a surface
in which the curvature radius in the YZ-plane and the curvature
radius in the XZ-plane, which perpendicularly intersects the
YZ-plane, are different from each other.
The above is a condition for correcting aberration which occurs
because the second surface is decentered or tilted with respect to
the visual axis. In general if a spherical surface is decentered,
the curvature relative to fight rays incident on the surface in the
plane of incidence and that in a plane perpendicularly intersecting
the incidence plane differ from each other. Therefore, in an ocular
optical system where a reflecting surface is disposed in front of
an observer's eyeball in such a manner as to be decentered or
tilted with respect to the visual axis as in the present invention,
an image on the visual axis lying in the center of the observation
image also has astigmatic aberration for the reason stated above.
In order to correct the axial astigmatism, it is important that any
one of the first, second and third surfaces of the ocular optical
system should be formed so that the curvature radius in the plane
of incidence and that in a plane perpendicularly intersecting the
incidence plane are different from each other.
Further, at least one of the surfaces constituting the ocular
optical system may be a free curved surface.
If at least one of at least three surfaces constituting the ocular
optical system is a free curved surface, it is possible to satisfy
the condition for obtaining the above-described effect produced by
an aspherical surface or an anamorphic surface, and hence possible
to effectively correct aberrations produced in the ocular optical
system.
Here, the free curved surface is a curved surface expressed by
##EQU1##
where x, y and z denote orthogonal coordinates, C.sub.nm is an
arbitrary coefficient, and k and k' are also arbitrary values,
respectively.
Further, it is desirable that the display surface of the image
display device should be tilted with respect to the axial principal
ray.
Examples 1 to 10 (described later) correspond to this
arrangement.
It is important that the display surface of the image display
device should be tilted with respect to the visual axis. In a case
where a refracting or reflecting surface which constitutes an
optical element is decentered or tilted, the refraction or
reflection angle of fight rays from the pupil at the refracting or
reflecting surface vary according to the image height, and the
image surface may be tilted with respect to the visual axis. In
such a case, the tilt of the image surface can be corrected by
tilting the display surface of the image display device with
respect to the visual axis.
Further, it is desirable that the image display device should be
disposed in such a manner that a side thereof which is reverse to
its display surface faces the observer.
Examples 1 to 10 (described later) correspond to this
arrangement.
An effective way of making the whole system compact is to dispose
the image display device in such a manner that a side thereof which
is reverse to its display surface faces the observer. In the case
of an image display device which has a back light and other
attachments provided behind it, these attachments are disposed
along the observer's face; therefore, no part of the image display
device projects forwardly beyond the ocular optical system In other
words, the whole image display apparatus can be arranged such that
the amount to which the optical system projects from the observer's
face is extremely small.
It should be noted that it becomes possible for the observer to see
a stable observation image by providing a device for positioning
both the image display device and the ocular optical system with
respect to the observer's head.
By allowing both the image display device and the ocular optical
system to be fitted to the observer's head with a supporting
device, it becomes possible for the observer to see the observation
image in a desired posture and from a desired direction.
Further, it becomes possible for the observer to enjoy viewing a
stereoscopic image with both eyes by providing a device for
supporting at least two image display apparatuses according to the
present invention at a predetermined spacing.
Further, if the ocular optical system of the image display
apparatus according to the present invention is arranged to form an
image of an object at infinity with the image display device
surface in the ocular optical system defined as an image surface,
the ocular optical system can be used as an imaging optical system,
e.g. a finder optical system for a camera such as that shown in
FIG. 19, as described later. Stiff other objects and advantages of
the invention will in part be obvious and will in part be apparent
from the specification.
The invention accordingly comprises the features of construction,
combinations of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an optical ray trace of Example 1 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 2 illustrates an optical ray trace of Example 2 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 3 illustrates an optical ray trace of Example 3 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 4 illustrates an optical ray trace of Example 4 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 5 illustrates an optical ray trace of Example 5 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 6 illustrates an optical ray trace of Example 6 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 7 illustrates an optical ray trace of Example 7 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 8 illustrates an optical ray trace of Example 8 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 9 illustrates an optical ray trace of Example 9 of an ocular
optical system in an image display apparatus according to the
present invention.
FIG. 10 illustrates an optical ray trace of Example 10 of an ocular
optical system in an image display apparatus according to the
present invention.
FIGS. 11a-11h is a pat of an aberration diagram illustrating
lateral aberrations in Example 1 of the present invention.
FIGS. 12a-12h is another part of the aberration diagram
illustrating lateral aberrations in Example 1 of the present
invention.
FIGS. 13a-13f is the other part of the aberration diagram
illustrating lateral aberrations in Example 1 of the present
invention.
FIGS. 14(a) and 14(b) are views used to explain internal reflection
at a first surface of an ocular optical system according to the
present invention.
FIGS. 15(a) and 15(b) are views used to explain the relationship
between total reflection and the configuration of a first surface
of an ocular optical system according to the present invention.
FIG. 16 shows the way of giving a definition of an incident angle
of an axial principal ray striking each surface.
FIGS. 17(a) and 17(b) are sectional and perspective views showing a
head-mounted image display apparatus according to the present
invention.
FIG. 18 shows an arrangement of an optical system according to the
present invention as it is used as an imaging optical system.
FIG. 19 shows an arrangement of an optical system according to the
present invention as it is used as an imaging optical system.
FIG. 20 shows the optical system of a conventional image display
apparatus.
FIGS. 21(a) and 21(b) show the optical system of another
conventional image display apparatus.
FIG. 22 shows the optical system of still another conventional
image display apparatus.
FIG. 23 shows the optical system of a further conventional image
display apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples 1 to 10 of image display apparatuses according to the
present invention will be described below with reference to the
accompanying drawings.
Constituent parameters of each example will be shown later. In the
following description, the surface Nos. are shown as ordinal
numbers in backward tracing from an observer's pupil position 1
toward an image display device 4 .Iadd.(image plane).Iaddend.. A
coordinate system is defined as follows: As shown in FIG. 1, with
the observer's iris position 1 defined as the origin, the direction
of an observer's visual axis 2 is taken as the Z-axis, where the
direction toward an ocular optical system 3 from the origin is
defined as the positive direction, and the vertical direction (as
viewed from the observer's eyeball) which perpendicularly
intersects the observer's visual axis 2 is taken as the Y-axis,
where the upward direction is defined as the positive direction.
Further, the horizontal direction (as viewed from the observer's
eyeball) which perpendicularly intersects the observer's visual
axis 2 is taken as the X-axis, where the leftward direction is
defined as the positive direction. That is, the plane of FIG. 1
(described later) is defined as the YZ-plane, and a plane which is
perpendicular to the plane of the figure is defined as the
XZ-plane. The optical axis is bent in the YZ-plane.
In the constituent parameters (shown later), regarding each surface
for which eccentricities Y and Z and inclination angle .theta. are
shown, the eccentricity Y is a distance by which the vertex of the
surface decenters in the Y-axis direction from the surface No. 1
(pupil position 1), which is a reference surface, and the
eccentricity Z is a distance by which the vertex of the surface
decenters in the Z-axis direction from the surface No. 1. The
inclination angle .theta. is the angle of inclination of the
central axis of the surface from the Z-axis. In this case, positive
.theta. means counterclockwise rotation. It should be noted that
the surface separation is meaningless.
The non-rotationally symmetric aspherical configuration of each
surface may be expressed in the coordinate system defining the
surface as follows: ##EQU2##
where R.sub.y is the paraxial curvature radius of each surface in
the YZ-plane (the plane of the figure); R.sub.x is the paraxial
curvature radius in the XZ-plane; K.sub.x is the conical
coefficient in the XZ-plane; K.sub.y is the conical coefficient in
the YZ-plane; AR and BR are 4th- and 6th-order aspherical
coefficients, respectively, which are rotationally symmetric with
respect to the Z-axis; and AP and BP are 4th- and 6th-order
aspherical coefficients, respectively, which are rotationally
asymmetric with respect to the Z-axis.
It should be noted that the refractive index of the medium between
a pair of surfaces is expressed by the refractive index for the
spectral d-line. Lengths are given in millimeters.
FIGS. 1 to 10 are sectional views of image display apparatuses
designed for a single eye according to Examples 1 to 10. In the
sectional views of FIGS. 1 to 5, reference numeral 1 denotes an
observer's pupil position, 2 an observer's visual axis, 3 an ocular
optical system 4 an image display device .Iadd.(image
plane).Iaddend., 5 a first surface of the ocular optical system 3,
6 a second surface of the ocular optical system 3, and 7 a third
surface of the ocular optical system 3.
In the sectional views of FIGS. 6 to 10, reference numeral 1
denotes an observer's pupil position, 2 an observer's visual axis,
3 an ocular optical system, 4 an image display device .Iadd.(image
plane).Iaddend., 11 a first surface of the ocular optical system 3,
12 a second surface of the ocular optical system 3, 13 a third
surface of the ocular optical system 3, and 14 a fourth surface of
the ocular optical system 3.
In these examples, the actual path of light rays is as follows: In
Examples 1 to 5, a bundle of light rays emitted from the image
display device 4 .Iadd.(image plane) .Iaddend.enters the ocular
optical system 3 while being refracted by the third surface 7 of
the ocular optical system 3. Then, the ray bundle is reflected by
the second surface 6, internally reflected by the first surface 5
and reflected by the second surface 6 again. Then, the ray bundle
is incident on the first surface 5 and exits from the ocular
optical system 3 while being refracted by the first surface 5 so as
to be projected into the observer's eyeball with the observer's
iris position or eyeball rolling center as the exit pupil 1.
In Examples 6 to 10, a bundle of light rays emitted from the image
display device 4 .Iadd.(image plane) .Iaddend.enters the ocular
optical system 3 while being refracted by the fourth surface 14 of
the ocular optical system 3. Then, the ray bundle is reflected by
the third surface 13, internally reflected by the first surface 11
and reflected by the second surface 12. Then, the ray bundle is
incident on the first surface 11 and exits from the ocular optical
system 3 while being refracted by the first surface 11 so as to be
projected into the observer's eyeball with the observer's iris
position or eyeball rolling center as the exit pupil 1.
The following examples are all image display apparatuses for the
right eye. An image display apparatus for the left eye can be
realized by disposing the constituent optical elements of each
example in symmetrical relation to the apparatus for the right eye
with respect to the YZ-plane.
In an actual apparatus, needless to say, the direction in which the
optical axis is beat by the ocular optical system may be any of the
upward and sideward directions of the observer.
The following is an explanation of the field angle, pupil diameter,
surface configuration of each surface, incident angle at each
surface and refractive index of a transparent medium in each
example.
Example 1 is one example of an ocular optical system comprising
three surfaces as shown in the sectional view of FIG. 1. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.8.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 5, the second
surface (surface Nos. 3 and 5) 6, and the third surface (surface
No. 6) 7 are all anamorphic surfaces. Internal reflection at the
first surface 5 is total reflection. Values for the conditions (1)
to (13) are as follows:
Example 2 is one example of an ocular optical system comprising
three surfaces as shown in the sectional view of FIG. 2. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.8.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 5 and the
second surface (surface Nos. 3 and 5) 6 are anamorphic surfaces,
and the third surface (surface No. 6) 7 is a spherical surface.
Internal reflection at the first surface 5 is total reflection.
Values for the conditions (1) to (13) are as follows:
Example 3 is one example of an ocular optical system comprising
three surfaces as shown in the sectional view of FIG. 3. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.8.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 5 and the
second surface (surface Nos. 3 and 5) 6 are anamorphic surfaces,
and the third surface (surface No. 6) 7 is a spherical surface.
Internal reflection at the first surface 5 is total reflection.
Values for the conditions (1) to (13) are as follows:
Example 4 is one example of an ocular optical system comprising
three surfaces as shown in the sectional view of FIG. 4. In this
example, the horizontal field angle is 28.degree., while the
vertical field angle is 21.2.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 5 and the
second surface (surface Nos. 3 and 5) 6 are anamorphic surfaces,
and the third surface (surface No. 6) 7 is a spherical surface.
Internal reflection at the first surface 5 is realized by mirror
coating. Values for the conditions (1) to (13) are as follows:
Example 5 is one example of an ocular optical system comprising
three surfaces as shown in the sectional view of FIG. 5. In this
example, the horizontal field angle is 28.degree., while the
vertical field angle is 21.2.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 5 is an
anamorphic surface. The second surface (surface Nos. 3 and 5) 6 is
a flat surface, and the third surface (surface No. 6) 7 is a
spherical surface. Internal reflection at the first surface 5 is
realized by mirror coating. Values for the conditions (1) to (13)
are as follows:
Example 6 is one example of an ocular optical system comprising
four surfaces as shown in the sectional view of FIG. 6. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.8.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 11 is a flat
surface, and the second surface (surface No. 3) 12, the third
surface (surface No. 5) 13 and the fourth surface (surface No. 6)
14 are anamorphic surfaces. Internal reflection at the first
surface 11 is total reflection. Values for the conditions (1) to
(13) are as follows:
Example 7 is one example of an ocular optical system comprising
four surfaces as shown in the sectional view of FIG. 7. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.8.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 11 is a
spherical surface. The second surface (surface No. 3) 12 and the
third surface (surface No. 5) 13 are anamorphic surfaces, and the
fourth surface (surface No. 6) 14 is a spherical surface. Internal
reflection at the first surface 11 is total reflection. Values for
the conditions (1) to (13) are as follows:
Example 8 is one example of an ocular optical system comprising
four surfaces as shown in the sectional view of FIG. 8. In this
example, the horizontal field angle is 40.degree., while the
vertical field angle is 30.6.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 11, the
second surface (surface No. 3) 12, the third surface (surface No.
5) 13 and the fourth surface (surface No. 6) 14 are all anamorphic
surfaces. Internal reflection at the first surface 11 is total
reflection. Values for the conditions (1) to (13) are as
follows:
Example 9 is one example of an ocular optical system comprising
four surfaces as shown in the sectional view of FIG. 9. In this
example, the horizontal field angle is 30.degree., while the
vertical field angle is 22.6.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 11 is a
spherical surface. The second surface (surface No. 3) 12 and the
third surface (surface No. 5) 13 are anamorphic surfaces, and the
fourth surface (surface No. 6) 14 is a spherical surface. Internal
reflection at the first surface 11 is realized by mirror coating.
Values for the conditions (1) to (13) are as follows:
Example 10 is one example of an ocular optical system comprising
four surfaces as shown in the sectional view of FIG. 10. In this
example, the horizontal field angle is 28.degree., while the
vertical field angle is 21.2.degree., and the pupil diameter is 4
millimeters. The first surface (surface Nos. 2 and 4) 11 is a
spherical surface. The second surface (surface No. 3) 12 and the
third surface (surface No. 5) 13 are anamorphic surfaces, and the
fourth surface (surface No. 6) 14 is a spherical surface. Internal
reflection at the first surface 11 is realized by mirror coating.
Values for the conditions (1) to (13) are as follows:
Values of constituent parameters in the above-described Examples 1
to 10 in backward ray tracing will be shown below.
Abbe's Sur- Surface Refractive No. (In- face Radius of separa-
index clination No. curvature tion (Eccentricity) angle) Example 1
1 .infin. (pupil) 2 R.sub.y -210.566 1.6481 55.28 R.sub.x -616.660
Y -26.631 .theta. 34.36.degree. K.sub.y 0 Z 3.827 K.sub.x 0 AR 0 BR
0 AP 0 BP 0 3 R.sub.y -130.170 1.6481 55.28 R.sub.x -131.141 Y
41.547 .theta. 10.87.degree. K.sub.y 0 Z 50.217 K.sub.x 0 AR
-2.8856 .times. 10.sup.-10 BR -2.3366 .times. 10.sup.-15 AP -4.1410
BP 5.4988 4 R.sub.y -210.566 1.6481 55.28 R.sub.x -616.660 Y
-26.631 .theta. 34.36.degree. K.sub.y 0 Z 3.827 K.sub.x 0 AR 0 BR 0
AP 0 BP 0 5 R.sub.y -130.170 1.6481 55.28 R.sub.x -131.141 Y 41.547
.theta. 10.87.degree. K.sub.y 0 Z 50.217 K.sub.x 0 AR -2.8856
.times. 10.sup.-10 BR -2.3366 .times. 10.sup.-15 AP -4.1410 BP
5.4988 6 R.sub.y -139.371 Y -39.978 .theta. 49.40.degree. R.sub.x
339.330 Z 67.618 K.sub.y 0 K.sub.x 0 AR 0 BR 0 AP 0 BP 0 7 (display
device) Y -46.520 .theta. 28.24.degree. Z 41.317 Example 2 1
.infin. (pupil) 2 R.sub.y -161.656 1.5163 64.15 R.sub.x -1301.410 Y
3.977 .theta. 26.73.degree. K.sub.y 0 Z 12.107 K.sub.x 0 AR 1.9502
.times. 10.sup.-7 BR -1.0740 .times. 10.sup.-11 AP 1.1334 BP 2.0740
3 R.sub.y -136.884 1.5163 64.15 R.sub.x -147.084 Y 4.315 .theta.
35.86.degree. K.sub.y -0.4474 Z 30.348 K.sub.x -1.1088 AR 5.6195
.times. 10.sup.-6 BR -8.8973 .times. 10.sup.-15 AP 2.6626 .times.
10.sup.-1 BP 7.2753 4 R.sub.y -161.656 1.5163 64.15 R.sub.x
-1301.410 Y 3.977 .theta. 26.73.degree. K.sub.y 0 Z 12.107 K.sub.x
0 AR 1.9502 .times. 10.sup.-7 BR -1.0740 .times. 10.sup.-11 AP
1.1334 BP 2.0740 5 R.sub.y -136.884 1.5163 64.15 R.sub.x -147.084 Y
4.315 .theta. 35.86.degree. K.sub.y -0.4474 Z 30.348 K.sub.x
-1.1088 AR 5.6195 .times. 10.sup.-6 BR -8.8973 .times. 10.sup.-15
AP 2.6626 .times. 10.sup.-1 BP 7.2753 6 192.794 Y -47.076 .theta.
79.13.degree. Z 41.366 7 (display device) Y -56.120 .theta.
38.58.degree. Z 39.788 Example 3 1 .infin. (pupil) 2 R.sub.y
-51.348 1.7433 44.75 R.sub.x -45.397 Y -8.790 .theta. 29.67.degree.
K.sub.y -0.0909 Z 1.764 K.sub.x 1.6087 AR -2.7583 .times. 10.sup.-6
BR -2.8974 .times. 10.sup.-10 AP -2.4093 BP 1.9705 3 R.sub.y
-57.489 1.7433 44.75 R.sub.x -53.053 Y 15.378 .theta. 32.14.degree.
K.sub.y -0.1177 Z 40.450 K.sub.x 0.1510 AR -5.1413 .times.
10.sup.-9 BR 4.8987 .times. 10.sup.-11 AP -7.1903 BP -4.2086
.times. 10.sup.-1 4 R.sub.y -51.348 1.7433 44.75 R.sub.x -45.397 Y
-8.790 .theta. 29.67.degree. K.sub.y -0.0909 Z 1.764 K.sub.x 1.6087
AR -2.7583 .times. 10.sup.-6 BR -2.8974 .times. 10.sup.-10 AP
-2.4093 BP 1.9705 5 R.sub.y -57.489 1.7433 44.75 R.sub.x -53.053 Y
15.378 .theta. 32.14.degree. K.sub.y -0.1177 Z 40.450 K.sub.x
0.1510 AR -5.1413 .times. 10.sup.-9 BR 4.8987 .times. 10.sup.-11 AP
-7.1903 BP -4.2086 .times. 10.sup.-1 6 -17.021 Y -21.771 .theta.
72.83.degree. Z 27.458 7 (display device) Y -35.479 .theta.
14.03.degree. Z 30.627 Example 4 1 .infin. (pupil) 2 R.sub.y
-408.985 1.5163 64.15 R.sub.x -283.326 Y -14.922 .theta.
24.30.degree. K.sub.y 0 Z 12.616 K.sub.x 0 AR -6.5368 .times.
10.sup.-6 BR 2.6628 .times. 10.sup.-11 AP -4.2799 .times. 10.sup.-2
BP 1.0453 3 R.sub.y -137.122 1.5163 64.15 R.sub.x 109.735 Y 5.062
.theta. 35.80.degree. K.sub.y -3.3707 Z 32.532 K.sub.x -2.6799 AR
9.0123 .times. 10.sup.-6 BR 5.8457 .times. 10.sup.-4 AP -3.5746
.times. 10.sup.-2 BP -9.1012 4 R.sub.y -408.985 1.5163 64.15
R.sub.x -283.326 Y 14.922 .theta. 24.30.degree. K.sub.y 0 Z 12.616
K.sub.x 0 AR -6.5368 .times. 10.sup.-6 BR 2.6628 .times. 10.sup.-11
AP -4.2799 .times. 10.sup.-2 BP 1.0453 5 R.sub.y -137.122 1.5163
64.15 R.sub.x -109.735 Y 5.062 .theta. 35.80.degree. K.sub.y
-3.3707 Z 32.532 K.sub.x -2.6799 AR 9.0123 .times. 10.sup.-6 BR
5.8457 .times. 10.sup.-14 AP -3.5746 .times. 10.sup.-2 BP -9.1012 6
39.708 Y -49.190 .theta. 66.30.degree. Z 52.374 7 (display device)
Y -50.195 .theta. 42.57.degree. Z 47.677 Example 5 1 .infin.
(pupil) 2 R.sub.y 155.857 1.5163 64.15 R.sub.x 108.364 Y -20.000
.theta. 30.81.degree. K.sub.y 0 Z 30.000 K.sub.x 0 AR -1.1508
.times. 10.sup.-7 BR 1.1468 .times. 10.sup.-10 AP -1.3330 BP
-1.7019 3 .infin. 1.5163 64.15 Y -1.565 .theta. 37.32.degree. Z
42.461 4 R.sub.y 155.857 1.5163 64.15 R.sub.x 108.364 Y -20.000
.theta. 30.81.degree. K.sub.y 0 Z 30.000 K.sub.x 0 AR -1.1508
.times. 10.sup.-7 BR 1.1468 .times. 10.sup.-10 AP -1.3330 BP
-1.7019 5 .infin. 1.5163 64.15 Y -1.565 .theta. 37.32.degree. Z
42.461 6 70.244 Y -33.253 .theta. 62.66.degree. Z 36.315 7 (display
device) Y -44.749 0 60.09 Z 55.961 Example 6 1 .infin. (pupil) 2
.infin. 1.4870 70.40 Y 0.000 .theta. 7.70.degree. Z 33.232 3
R.sub.y -92.681 1.4870 70.40 R.sub.x -91.368 Y 10.225 .theta.
37.34.degree. K.sub.y 2.9442 Z 34.669 K.sub.x -6.4492 AR 6.7868
.times. 10.sup.-6 BR 1.2064 .times. 10.sup.-12 AP 1.1032 .times. 10
BP -3.6642 4 .infin. 1.4870 70.40 Y 0.000 .theta. 7.70.degree. Z
33.232 5 R.sub.y -227.431 1.4870 70.40 R.sub.x -73.582 Y 30.000
.theta. 48.36.degree. K.sub.y 0 Z 2.395 K.sub.x 0 AR 4.6395 .times.
10.sup.-7 BR 1.1004 .times. 10.sup.-11 AP 5.1263 .times. 10 BP
-3.0762 6 R.sub.y 66.981 R.sub.x 16.415 Y -36.765 .theta.
57.28.degree. K.sub.y 0 Z 69.400 K.sub.x 0 AR 2.2637 .times.
10.sup.-6 BR -7.3017 .times. 10.sup.-8 AP -3.7748 .times. 10.sup.-1
BP -6.6901 .times. 10.sup.-1 7 (display device) Y -33.673 .theta.
45.00.degree. Z 44.201 Example 7 1 .infin. (pupil) -542.306 1.5163
64.15 Y 70.778 .theta. 5.68.degree. Z 30.533 3 R.sub.y -105.705
1.4870 70.40 R.sub.x -89.941 Y 10.225 .theta. 37.34.degree. K.sub.y
-0.1753 Z 34.669 K.sub.x -0.8315 AR 3.6313 .times. 10.sup.-6 BR
6.1440 .times. 10.sup.-12 AP -8.7199 .times. 10.sup.-2 BP -5.0996
.times. 10 4 -542.306 1.5163 64.15 Y 70.778 5.68.degree. Z 30.533 5
R.sub.y -180.609 1.5163 64.15 R.sub.x -1143.935 Y 40.198 .theta.
41.35.degree. K.sub.y 0.1463 Z 16.177 K.sub.x -1488.0941 AR 2.0564
.times. 10.sup.-6 BR 5.2529 .times. 10.sup.-14 AP -3.7942 .times.
10.sup.-2 BP 3.6207 6 -74.701 Y -39.077 .theta. 34.94.degree. Z
47.282
7 (display device) Y -36.693 24.18.degree. Z 36.463 Example 8 1
.infin. (pupil) 2 R.sub.y -245.203 1.5338 65.89 R.sub.x -52.851 Y
0.000 20.00.degree. K.sub.y 0 Z -1.281 AR 0 BR 0 AP 0 BP 0 3
R.sub.y -59.102 1.5163 64.15 R.sub.x -45.130 Y 4.315 .theta.
35.86.degree. K.sub.y -0.9559 Z 30.348 K.sub.x -0.2970 AR 6.4446
.times. 10.sup.-6 BR 9.3898 .times. 10.sup.-14 AP 7.4590 BP -1.3817
.times. 10 4 R.sub.y -245.203 1.5338 65.89 R.sub.x -52.851 Y 0.000
.theta. 20.00.degree. K.sub.y 0 Z -1.281 AR 0 BR 0 AP 0 BP 0 5
R.sub.y -92.593 1.5338 65.89 R.sub.x -71.241 Y 29.319 .theta.
41.82.degree. K.sub.y 0 Z -4.482 K.sub.x 0 AR 7.6834 .times.
10.sup.-7 BR 1.6178 .times. 10.sup.-11 AP 4.2887 .times. 10.sup.-1
BP -3.0887 6 R.sub.y -72.841 R.sub.x 81.858 Y -28.655 .theta.
22.75.degree. K.sub.y 0 Z 36.867 K.sub.x 0 AR 6.7391 .times.
10.sup.-7 BR -4.2424 .times. 10.sup.-10 AP -1.1564 .times. 10 BP
-8.0054 7 (display device) Y -28.600 35.00.degree. Z 19.053 Example
9 1 .infin. (pupil) 2 64.328 1.5163 64.15 Y -20.000 .theta.
30.00.degree. Z 27.699 3 R.sub.y 139.632 1.5163 64.15 R.sub.x
277.392 Y 0.129 39.41.degree. K.sub.y -10.6785 Z 35.000 K.sub.x
20.0000 AR -7.5208 .times. 10.sup.-6 BR 9.3767 .times. 10.sup.-13
AP 3.6868 BP -6.5396 4 64.328 1.5163 64.15 Y -20.000 .theta.
30.00.degree. Z 27.699 5 R.sub.y 61.956 1.5163 64.15 R.sub.x 70.808
Y -2.352 36.43.degree. K.sub.y 0 Z 27.385 K.sub.x 0 AR 3.5927
.times. 10.sup.-7 BR -4.9429 .times. 10.sup.-10 AP -1.7527 BP
-9.8564 .times. 10.sup.-2 6 45.850 Y -33.382 .theta. 72.85.degree.
Z 36.018 7 (display device) Y -38.077 .theta. 84.87.degree. Z
57.285 Example 10 1 .infin. (pupil) 2 68.114 1.5163 64.15 Y -7.666
.theta. 30.00.degree. Z 24.886 3 R.sub.y 172.006 1.5163 64.15
R.sub.x 230.352 Y 3.180 .theta. 39.16.degree. K.sub.y 20.0000 Z
40.000 K.sub.x -20.0000 AR 1.9117 .times. 10.sup.-6 BR -8.7696
.times. 10.sup.-10 AP -7.5555 .times. 10.sup.-1 BP -1.2220 4 68.114
1.5163 64.15 Y -7.666 .theta. 30.00.degree. Z 24.886 5 R.sub.y
-150.750 1.5163 64.15 R.sub.x -87.182 Y 3.180 .theta. 39.16.degree.
K.sub.y -79.4956 Z 40.000 K.sub.x -334.5455 AR 8.5541 .times.
10.sup.-7 BR -1.7073 .times. 10.sup.-10 AP 4.0595 .times. 10.sup.-1
BP 8.1476 .times. 10.sup.-2 -5.311 Y 30.000 .theta. 67.19.degree. Z
44.886 7 (display device) Y -36.353 .theta. 60.00 Z 51.966
FIGS. 11 to 13 graphically show lateral aberrations in Example 1
among the above-described Examples 1 to 10. In these aberrational
diagrams, the parenthesized numerals denote (horizontal field
angle, and vertical field angle), and lateral aberrations at the
field angles are shown.
Although in the above-described examples anamorphic surfaces,
spherical surfaces and flat surfaces are used for the constituent
surfaces, it should be noted that these surfaces may have other
surface configurations, e.g. toric surfaces, rotationally symmetric
aspherical and spherical surfaces, and free curved surfaces defined
by the expression (14). It is also possible to use holographic
surfaces for the constituent surfaces.
In the case of a surface configuration for which curvature, power,
etc. cannot be defined, the curvature, power, etc. of the surface
may be obtained by determining the curvature in an arbitrary region
which is obtained from the differential of the configuration of a
portion of the surface at the intersection between the surface and
axial light rays extending on the visual axis to reach the image
display device, along the axial light rays, and defining the
obtained curvature as the curvature of that surface.
Incidentally, it is possible to form a portable image display
apparatus, such as a stationary or head-mounted image display
apparatus, which enables the observer to see with both eyes, by
preparing a combination of an image display device and an ocular
optical system according to the present invention, arranged as
described above, for each of the left and right eyes, and
supporting the two combinations apart from each other by the
interpupillary distance, that is, the distance between the eyes. It
should be noted that it is also possible to form an image display
apparatus for a single eye in which an ocular optical system
according to the present invention is disposed for a single eye of
the observer.
To arrange the image display apparatus of the present invention as
a head-mounted image display apparatus (HMD) 31, as shown in the
sectional view of FIG. 17(a) and the perspective view of FIG.
17(b), the HMD 31 is fitted to the observer's head by using a
headband 20, for example, which is attached to the HMD 31. In this
example of use, the HMD 31 may be arranged such that the second
surface 6 of the ocular optical system 3 is formed by using a
semitransparent mirror (half-mirror), and a see-through
compensating optical system 22 and a liquid crystal shutter 21 are
provided in front of the half-mirror, thereby enabling an outside
world image to be selectively observed or superimposed on the image
of the image display device 4. In this case, the see-through
compensating optical system 22 comprises a transparent prism member
which has been set so that the power of the entire optical system
is approximately zero with respect to light from the outside
world.
Further, the ocular optical system of the image display apparatus
according to the present invention can be used as an imaging
optical system. For example, as shown in the perspective view of
FIG. 18, the ocular optical system may be used in a finder optical
system F.sub.i of a compact camera C.sub.a in which a photographic
optical system O.sub.b and the finder optical system F.sub.i are
provided separately in parallel to each other. FIG. 19 shows the
arrangement of an optical system in a case where the ocular optical
system according to the present invention is used as such an
imaging optical system. As illustrated, an ocular optical system DS
according to the present invention is disposed behind a front lens
group GF and an aperture diaphragm D, thereby constituting an
objective optical system L.sub.r. An image .Iadd.(image plane)
.Iaddend.that is formed by the objective optical system L.sub.r is
erected by a Porro prism P, in which there are four reflections,
provided at the observer side of the objective optical system
L.sub.r, thereby enabling an erect image to be observed through an
ocular lens O.sub.c.
Although the image display apparatus according to the present
invention has been described by way of examples, it should be noted
that the present invention is not necessarily limited to these
examples and that various changes and modifications may be imparted
thereto.
As will be clear from the foregoing description, the image display
apparatus according to the present invention makes it possible to
provide an image display apparatus which has a wide field angle for
observation and is extremely small in size and light in weight.
* * * * *