U.S. patent number RE37,292 [Application Number 09/315,990] was granted by the patent office on 2001-07-24 for optical system and optical apparatus.
This patent grant is currently assigned to Olympus Optical Co., Ltd.. Invention is credited to Koichi Takahashi, Takayoshi Togino.
United States Patent |
RE37,292 |
Togino , et al. |
July 24, 2001 |
Optical system and optical apparatus
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 light in weight. The image display apparatus has an
image display device (7) and an ocular optical system (8) for
projecting the image of the image display device (7) and leading
the projected image to an observer's eyeball (1). The ocular
optical system (8) has at least three optical surfaces, and a space
formed by these surfaces is filled with a medium having a
refractive index larger than 1. The three optical surfaces are
defined as a first surface (3), a second surface (4), and a third
surface (5), respectively, in the order in which light rays pass in
backward ray tracing from the observer's eyeball (1) to the image
display device (7). The optical surfaces are disposed such that
light rays from the observer's eyeball (1) pass through the first
surface (3) and are reflected by the second surface (4) and further
reflected by the third surface (5), which is a reflecting surface
having positive power, and the light rays reflected by the third
surface (5) are reflected by the first surface (3) and pass through
the second surface (4) to reach the image display device (7).
Inventors: |
Togino; Takayoshi (Koganei,
JP), Takahashi; Koichi (Hachioji, JP) |
Assignee: |
Olympus Optical Co., Ltd.
(Tokyo, JP)
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Family
ID: |
16052298 |
Appl.
No.: |
09/315,990 |
Filed: |
May 21, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
678970 |
Jul 12, 1996 |
05748378 |
May 5, 1998 |
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Foreign Application Priority Data
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Jul 14, 1995 [JP] |
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7-178657 |
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Current U.S.
Class: |
359/633;
359/630 |
Current CPC
Class: |
G02B
17/0832 (20130101); G02B 17/086 (20130101); G02B
27/0172 (20130101); G02B 2027/011 (20130101); G02B
2027/0132 (20130101); G02B 2027/0178 (20130101) |
Current International
Class: |
G02B
27/01 (20060101); G02B 17/08 (20060101); G02B
27/00 (20060101); G02B 027/14 () |
Field of
Search: |
;359/630,631,633,636,637,638,640 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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62-214782 |
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Sep 1987 |
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JP |
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3-101709 |
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Apr 1991 |
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JP |
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8-248481 |
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Sep 1996 |
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JP |
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Primary Examiner: Mack; Ricky
Attorney, Agent or Firm: Pillsbury Madison & Sutro
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 displayed by said image display device and for
leading the projected, image to an observer's eyeball,
said ocular optical system having at least three optical surfaces,
wherein a space formed by said at least three optical surfaces is
filled with a medium having a refractive index larger than 1,
said at least three optical surfaces being defined as a first
surface, a second surface, and a third surface, respectively, in
order in which light rays pass in backward ray tracing from said
observer's eyeball to said image display device, and
said at least three optical surfaces being disposed such that light
rays pass in said backward ray tracing from said observer's eyeball
pass through the first surface and are reflected by the second
surface and further reflected by the third surface, which is a
reflecting surface having positive power, and the light rays
reflected by said third surface are reflected by said first surface
and pass through said second surface to reach said image display
device.
2. An image display apparatus according to claim 1, wherein the
reflection at said first surface is total reflection.
3. An image display apparatus according to claim 1 or 2, wherein
said third surface is disposed such that light rays on an
observer's visual axis which have been reflected by said second
surface are tilted at approximately 30.degree. toward said
observer's eyeball by reflection at said third surface.
4. An image display apparatus according to claim 3, which satisfies
the following condition:
where .theta..sub.1 is a tilt angle of said light rays.
5. An image display apparatus according to claim 3, which satisfies
the following condition:
where .theta..sub.1 is a tilt angle of said light rays.
6. An image display apparatus according to claim 1 or 2, which
satisfies the following condition:
where .theta..sub.2 is an angle between said first surface and said
second surface.
7. An image display apparatus according to claim 1 or 2, wherein
internal reflection at said second surface is total reflection.
8. An image display apparatus comprising an image display device
for displaying an image, and an ocular optical system for
projecting the image displayed by said image display device and for
leading the projected image to an observer's eyeball,
said ocular optical system having at least four optical surfaces,
wherein a space formed by said at least four optical surfaces is
filled with a medium having a refractive index larger than 1,
said at least four optical surfaces being defined as a first
surface, a second surface, a third surface, and a fourth surface,
respectively, in order in which light rays pass in backward ray
tracing from said observer's eyeball to said image display device,
and
said at least four optical surfaces being disposed such that light
rays pass in backward ray tracing from said observer's eyeball pass
through the first surface and are reflected by the second surface
and further reflected by the third surface, which is a reflecting
surface having positive power, and the light rays reflected by said
third surface are reflected by said first surface and pass through
the fourth surface to reach said image display device.
9. An image display apparatus according to claim 8, wherein the
reflection at said first surface is total reflection.
10. An image display apparatus according to claim 8 or 9, wherein
said third surface is disposed such that light rays on an
observer's visual axis which have been reflected by said second
surface are tilted at approximately 30.degree. toward said
observer's eyeball by reflection at said third surface.
11. An image display apparatus according to claim 10, which
satisfies the following condition:
where .theta..sub.1 is a tilt angle of said light rays.
12. An image display apparatus according to claim 10, which
satisfies the following condition:
where .theta..sub.1 is a tilt angle of said light rays.
13. An image display apparatus according to claims 8 or 9, which
satisfies the following condition:
where .theta..sub.2 is an angle between said first surface and said
second surface.
14. An image display apparatus according to claim 1, 2, 8 or 9,
wherein at least one optical boundary surface is disposed in an
optical path of said optical system.
15. An image display apparatus according to claim 1, 2, 8 or 9,
further comprising means for positioning both said image display
device said ocular optical system with respect to an observer's
head.
16. An image display apparatus according to claim 1, 2, 8 or 9,
further comprising means for supporting both said image display
device and said ocular optical system with respect to an observer's
head so that said image display apparatus can be fitted to said
observer's head.
17. An image display apparatus according to claim 1, 2, 8 or 9,
further comprising means for supporting at least a pair of said
image display apparatuses at a predetermined spacing.
18. An image display apparatus according to claim 1, 2, 8 or 9,
wherein said ocular optical system is used as an imaging optical
system..Iadd.
19. An ocular optical system disposed between an image plane and a
pupil,
said optical system comprising a prism member having at least three
surfaces including a first surface, a second surface, and a third
surface, wherein a space formed by said at least three surfaces is
filled with a medium having a refractive index larger than 1,
wherein said prism member is arranged such that light rays as
traced from said image plane toward said pupil first pass through
said second surface and are then reflected by said first surface
and further reflected by said third surface, and the reflected
light rays are reflected by said second surface and pass through
said first surface, and/or such that light rays as traced from said
pupil toward said image plane first pass through said first surface
and are then reflected by said second surface and further reflected
by said third surface, and the reflected light rays are reflected
by said first surface and pass through said second surface, and
wherein at least one of said first surface, said second surface and
said third surface is a curved surface..Iaddend..Iadd.
20. An ocular optical system according to claim 19, wherein said
first surface is positioned to face opposite to said image
plane..Iaddend..Iadd.
21. An ocular optical system according to claim 19, wherein said
first surface has a curved surface configuration which gives a
positive power to the light rays when reflected by said first
surface..Iaddend..Iadd.
22. An ocular optical system according to claim 19, wherein said
second surface has a curved surface configuration which gives a
positive power to the light rays when reflected by said second
surface..Iaddend..Iadd.
23. An ocular optical system according to claim 19, wherein said
third surface has a curved surface configuration which gives a
positive power to the light rays when reflected by said third
surface..Iaddend..Iadd.
24. An ocular optical system according to claim 19, 20, 21, 22 or
23, wherein said prism member inverts the image formed on said
image plane, upside down..Iaddend..Iadd.
25. An ocular optical system according to claim 24, wherein said
first surface has a rotationally asymmetric curved surface
configuration having an action by which decentration aberrations
are corrected..Iaddend..Iadd.
26. An ocular optical system according to claim 24, wherein said
third surface has a rotationally asymmetric curved surface
configuration having an action by which decentration aberrations
are corrected..Iaddend..Iadd.
27. An ocular optical system according to claim 24, wherein said
first surface is formed from a spherical
surface..Iaddend..Iadd.
28. An ocular optical system according to claim 24, wherein said
second surface is formed from a spherical
surface..Iaddend..Iadd.
29. An ocular optical system according to claim 24, wherein said
third surface is formed from a spherical
surface..Iaddend..Iadd.
30. An ocular optical system according to claim 24, wherein
reflection at said first surface is total
reflection..Iaddend..Iadd.
31. An ocular optical system according to claim 24, wherein
reflection at said second surface is total
reflection..Iaddend..Iadd.
32. An ocular optical system according to claim 24, wherein said
prism member is arranged such that a spacing between said first
surface and second surface gradually increases toward said third
surface..Iaddend..Iadd.
33. An ocular optical system according to claim 24, which satisfies
the following condition:
where .theta..sub.2 is an angle formed between said first surface
and said second surface..Iaddend..Iadd.
34. An ocular optical system according to claim 24, further
comprising a lens disposed between said prism member and said image
plane..Iaddend..Iadd.
35. An ocular optical system according to claim 34, wherein said
lens is cemented to said second surface of said prism
member..Iaddend..Iadd.
36. An ocular optical system according to claim 24, wherein a field
angle in a horizontal direction of said prism member is different
from a field angle in a vertical direction
thereof..Iaddend..Iadd.
37. An ocular optical system according to claim 24, wherein the
field angle in the horizontal direction of said prism member is
larger than the field angle in the vertical direction
thereof..Iaddend..Iadd.
38. An image-forming optical system which forms an image of an
object,
said image-forming optical system comprising at least one prism
member,
wherein said prism member has at least three optical surfaces,
wherein a space formed by said at least three optical surfaces is
filled with a medium having a refractive index larger than 1, and
said at least three optical surfaces are defined as a first
surface, a second surface, and a third surface, respectively, in
order of ray tracing from the object to an image plane,
said at least three optical surfaces being disposed such that light
rays from said object pass through said first surface and are then
reflected by said second surface and further reflected by said
third surface, and the reflected light rays are reflected by said
first surface and pass through said second surface to reach said
image plane, and
wherein at least one of said first surface, said second surface and
said third surface is formed from a curved surface to give a
positive power to the light rays when reflected by said at least
one surface..Iaddend..Iadd.
39. An image-forming optical system according to claim 38, wherein
said first surface is positioned to face opposite to said image
plane..Iaddend..Iadd.
40. An image-forming optical system according to claim 38, wherein
said first surface has a curved surface configuration which gives a
positive power to the light rays when reflected by said first
surface..Iaddend..Iadd.
41. An image-forming optical system according to claim 38, wherein
said second surface has a curved surface configuration which gives
a positive power to the light rays when reflected by said second
surface..Iaddend..Iadd.
42. An image-forming optical system according to claim 38, wherein
said third surface has a curved surface configuration which gives a
positive power to the light rays when reflected by said third
surface..Iaddend..Iadd.
43. An image-forming optical system according to claim 38, 39, 40,
41 or 42, wherein reflection at least one of said first surface and
second surface is total reflection..Iaddend..Iadd.
44. An image-forming optical system according to claim 43, wherein
said first surface has a rotationally asymmetric curved surface
configuration having an action by which decentration aberrations
are corrected..Iaddend..Iadd.
45. An image-forming optical system according to claim 43, wherein
said third surface has a rotationally asymmetric curved surface
configuration having an action by which decentration aberrations
are corrected..Iaddend..Iadd.
46. An image-forming optical system according to claim 43, wherein
said first surface is formed from a spherical
surface..Iaddend..Iadd.
47. An image-forming optical system according to claim 43, wherein
said second surface is formed from a spherical
surface..Iaddend..Iadd.
48. An image-forming optical system according to claim 43, wherein
said third surface is formed from a spherical
surface..Iaddend..Iadd.
49. An image-forming optical system according to claim 43, wherein
said prism member is arranged such that a spacing between said
first surface and said second surface gradually increases toward
said third surface..Iaddend..Iadd.
50. An image-forming optical system according to claim 43, which
satisfies the following condition:
where .theta..sub.2 is an angle formed between said first surface
and said second surface..Iaddend..Iadd.
51. An image-forming optical system according to claim 43, further
comprising a lens disposed between said prism member and said image
plane..Iaddend..Iadd.
52. An image-forming optical system according to claim 51, wherein
said lens is cemented to said second surface of said prism
member..Iaddend..Iadd.
53. An image-forming optical system according to claim 43, wherein
a field angle in a horizontal direction of said prism member is
different from a field angle in a vertical direction
thereof..Iaddend..Iadd.
54. An image-forming optical system according to claim 43, wherein
the field angle in the horizontal direction of said prism member is
larger than the field angle in the vertical direction
thereof..Iaddend..Iadd.
55. A camera apparatus according to claim 43, wherein said
image-forming optical system is disposed to perform image
formation..Iaddend..Iadd.
56. A camera apparatus according to claim 55, wherein a
photographic optical system and a finder optical system are
disposed separately from each other..Iaddend..Iadd.
57. A camera apparatus according to claim 56, wherein said
image-forming optical system is disposed in said finder optical
system..Iaddend..Iadd.
58. A camera apparatus according to claim 57, wherein said finder
optical system includes, in order from an object side thereof, said
image-forming optical system; an image erecting optical system for
erecting the object image formed by said image-forming optical
system; and an ocular optical system for observing said object
image..Iaddend..Iadd.
59. An optical system disposed between an image plans and a
pupil,
said optical system comprising at least one prism member,
said prism member having at least three reflecting surfaces that
reflect a light beam in said prism member, said three reflecting
surfaces being so arranged that optical paths intersect each other
in said prism member,
wherein at least one of said at least three reflecting surfaces has
a curved surface configuration..Iaddend..Iadd.
60. An optical system according to claim 59, wherein said at least
three reflecting surfaces of said prism member are curved
surfaces..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. 13(a) shows the entire optical system of the
conventional image display apparatus, and FIG. 13(b) shows a part
of an ocular optical system used in the image display apparatus. As
illustrated in these figures, 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.
U.S. Pat. No. 4,669,810 discloses another type of conventional
image display apparatus. In this apparatus, as shown in FIG. 14, an
image of a CRT is transmitted through a relay optical system to
form an intermediate image, and the image is projected into an
observer's eye by a combination of a reflection holographic element
and a combiner having a hologram surface.
Japanese Patent Application Unexamined Publication (KOKAI) No.
62-214782 (1987) discloses another type of conventional image
display apparatus. As shown in FIGS. 15(a) and 15(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. 16, 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. 17, the
apparatus is an ocular optical system designed to project an object
surface onto an exit pupil by a semitransparent concave mirror and
a semitransparent plane mirror.
Other known image display apparatuses include those which are
disclosed in U.S. Pat. Nos. 4,081,209, 4,969,724 and 5,000,544.
In image display apparatuses of the type wherein an image of an
image display device is relayed, as shown in FIGS. 13(a), 13(b) and
14, aberration produced by the ocular optical system can be
corrected by the relay optical system, and it is possible to effect
favorable aberration correction in the optical system as a whole.
However, several lenses must be used as the relay optical system in
addition to the ocular optical system. Consequently, the optical
path length increases, and the optical system increases in both
size and weight.
In a case where only the ocular optical system shown in FIG. 13(a)
is used, as shown in FIG. 13(b), positive power resides in only the
reflecting surface that has a concave surface directed toward the
observer. Therefore, large negative field curvature is produced as
shown by reference character P1 in the figure.
In a layout such as that shown in FIG. 15, the amount to which the
apparatus projects from the observer's face undesirably increases.
Further, because 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.
Because 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 arrangement
of the optical system.
However, if an ordinary reflecting concave magnifier alone is used
as an ocular optical system, exceedingly large aberrations are
produced, and there is no device for correcting them. Even if axial
spherical aberration can be corrected by forming the configuration
of the concave surface of the magnifier into an aspherical surface,
off-axis aberrations such as coma, field curvature and astigmatism
remain. Therefore, if the field angle 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. 16.
In a coaxial ocular optical system in which an object surface is
projected onto an observer's pupil by using a semitransparent
concave mirror and a semitransparent plane mirror, as shown in FIG.
17, because 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, because field curvature that is
produced by the semitransparent 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.
To attain the above-described object, the present invention
provides an image display apparatus which includes an image display
device for displaying an image, and an ocular optical system for
projecting the image displayed by the image display device and for
leading the projected image to an observer's eyeball. The ocular
optical system has at least three optical surfaces, and a space
formed by the at least three optical surfaces is filled with a
medium having a refractive index larger than 1. The at least three
optical surfaces are defined as a first surface, a second surface,
and a third surface, respectively, in the order in which light rays
pass in backward ray tracing from the observer's eyeball to the
image display device. The at least three optical surfaces are
disposed such that light rays from the observer's eyeball pass
through the first surface and are reflected by the second surface
and further reflected by the third surface, which is a reflecting
surface having positive power, and the light rays reflected by the
third surface are reflected by the first surface and pass through
the second surface to reach the image display device.
In this case, the reflection at the first surface is preferably
total reflection.
In addition, the present invention provides an image display
apparatus which includes an image display device for displaying an
image, and an ocular optical system for projecting the image
displayed by the image display device and for leading the projected
image to an observer's eyeball. The ocular optical system has at
least four optical surfaces, and a space formed by the at least
four optical surfaces is filled with a medium having a refractive
index larger than 1. The at least four optical surfaces are defined
as a first surface, a second surface, a third surface, and a fourth
surface, respectively, in the order in which light rays pass in
backward ray tracing from the observer's eyeball to the image
display device. The at least four optical surfaces are disposed
such that the light rays from the observer's eyeball pass through
the first surface and are reflected by the second surface and
further reflected by the third surface, which is a reflecting
surface having positive power, and the light rays reflected by the
third surface are reflected by the first surface and pass through
the fourth surface to reach the image display device.
The operation of the above-described image display apparatus
according to the present invention 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 present invention, 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, thereby
making it possible to correct spherical aberration, coma and field
curvature produced by the third surface, which is decentered and
tilted, and thus succeeding in providing the observer with a clear
observation image having a wide exit pupil diameter and a wide
field angle.
Concave mirrors generally have such nature that, if strong power is
given to the concave surface, Petzval sum increases, and positive
field curvature is produced. When the pupil position is far away
from the curvature center of the concave mirror, negative comatic
aberration is produced. However, in order to provide an image
display apparatus which is compact and yet provides a wide field
angle, it is important to enlarge an image of a small image display
device by an optical system which has a short focal length, that
is, strong positive power.
The present invention meets the inconsistent demands that the image
display apparatus should be compact and provide a wide field angle
and yet have minimal aberration by filling the space formed by the
first, second and third surfaces with a medium having a refractive
index larger than 1.
By filling the space formed by the three surfaces with a medium
having a refractive index larger than 1, it becomes possible to
effectively use the space where light rays pass through the first
surface when entering the ocular optical system and pass through
the second surface when emanating from the ocular optical system.
In this case, light rays from the pupil are convergently refracted
by the first surface. Therefore, it is possible to suppress the
divergence of light rays in the optical system and prevent
vignetting of light rays.
In addition it is possible to minimize the height at which
extra-axial principal and subordinate rays are incident on the
third surface. Consequently, it is possible to minimize the
effective apertures of the second and third surfaces and to reduce
the size of the ocular optical system. At the same time, field
curvature is reduced, and it becomes possible to widen the field
angle. Further, the optical path length between the concave mirror
and the pupil position can be made longer than the mechanical
length. In other words, the pupil position can be set away from the
optical system to obtain a relatively long eye point, and yet,
optically, the pupil can be disposed in the vicinity of the
curvature center of the concave mirror. Thus, it is possible to
reduce comatic aberration produced by the third surface.
In the present invention, after passing through the first surface,
light rays are reflected by the second surface and further
reflected by the third surface, which has positive power.
Thereafter, the light rays are reflected by the first surface and
pass through the second surface. Accordingly, the optical path can
be bent in a compact form in an optical element having small
volumetric capacity.
In the optical system, because a principal surface having positive
refractive power is formed from a reflecting surface, chromatic
aberration produced in the optical system is minimized in theory.
Accordingly, it is unnecessary to correct chromatic aberration by
using glass materials having different Abbe's numbers. Thus, it
becomes possible to form the optical system of a single vitreous
material.
If the system is arranged such that the light rays reflected by the
third surface are totally reflected by the first surface, the size
of the ocular optical system can be effectively reduced. This will
be explained below in detail.
FIGS. 11(a) and 11(b) are sectional views each illustrating an
optical path in the image display apparatus according to the
present invention. FIG. 11(a) shows an ocular optical system in
which a first surface 3 does not totally reflect light rays. FIG.
11(b) shows an ocular optical system in which total reflection
occurs at a first surface 3. In these sectional views, reference
numeral 1 denotes an observer's pupil position, 2 an observer's
visual axis, 3 a first surface of the ocular optical system, 4 a
second surface of the ocular optical system, 5 a third surface of
the ocular optical system, and 7 an image display device. In FIG.
11(a), an internally reflecting region M of the first surface 3 has
been mirror-coated. The other region of the first surface 3 is a
region having no mirror coating.
In backward ray tracing, light rays coming out of the pupil 1 enter
the first surface 3 of the ocular optical system. The incident
light rays are refracted by the first surface 3 and then reflected
by the second surface 4. The reflected light rays are further
reflected by the third surface 5. In the arrangement shown in FIG.
11(a), there is no overlap between a reflecting region of the first
surface 3 where lower extra-axial light rays L are reflected and a
transmitting region of the first surface 3 where the lower
extra-axial light rays L pass. Therefore, it is necessary to
increase the height of the ocular optical system. That is, when the
reflecting region and the transmitting region are formed separately
from each other, it is difficult to form a compact optical
system.
In other words, if the size of the ocular optical system is kept
constant, it is possible to widen the field angle for observation,
particularly the vertical field angle, by dividing the transmitting
and reflecting regions from each other.
Therefore, the ocular optical system according to the present
invention is arranged such that, as shown in FIG. 11(b), the
transmitting region of the first surface 3 for light rays including
upper extra-axial light rays U and lower extra-axial light rays L
and the reflecting region of the first surface 3 for light rays
including upper extra-axial light rays U and lower extra-axial
light rays L are approximately coincident with each other, thereby
succeeding in reducing the size of the optical system.
If the internal reflection at the first surface 3 satisfies the
condition for total reflection, the first surface 3 need not be
mirror-coated. Therefore, even if a ray bundle passing through the
first surface 3 and a ray bundle reflected by the first surface 3
interfere with each other at the first surface 3, the light rays
can perform their original functions.
It is preferable to dispose the third surface 5 such that, after
being reflected by the second surface 4, light rays on the
observer's visual axis 2 are tilted at approximately 30.degree.
toward the observer's eyeball by reflection at the third surface 5.
At the third surface 5, which is a concave mirror having positive
power, as the reflection angle becomes larger, comatic aberration
due to decentration occurs to a larger extent. Conversely, if the
angle of reflection at the third surface 5 is not sufficiently
large, the light rays reflected by the third surface 5 cannot be
internally reflected by the first surface 3.
In order that the light rays reflected by the third surface 5 shall
be reflected by the first surface 3 with a practically admitted
amount of aberration, it is desirable to dispose the third surface
5 such that the above-described tilt angle is approximately
30.degree..
It is more desirable to satisfy the following condition:
where .theta..sub.1 is the tilt angle of the light rays.
The condition (1) shows practical limits of the condition for
attaining the above-described purposes. If .theta..sub.1 is not
larger than the lower limit of the condition (1), i.e. 20.degree.,
as shown in the sectional view of FIG. 12, light rays reflected by
the third surface 5 cannot be reflected by the first surface 3; the
reflected light rays undesirably return to and pass through the
second surface 4. In this case, the second surface 4 must be formed
by using a semitransparent surface, and the transmittance of the
optical system undesirably reduces. If .theta..sub.1 is not smaller
than the upper limit of the condition (1), i.e. 45.degree., comatic
aberration is produced by the third surface 5 becomes excessively
large and hence impossible to correct by another surface.
In order to minimize the optical path passing through the prism
constituting the ocular optical system and to make the whole
optical system even more compact, it is desirable to restrict the
range defined by the condition (1) to the range defined by the
following condition (1'):
It is also desirable to satisfy the following condition:
wherein .theta..sub.2 is the angle between the first and second
surfaces 3 and 4.
If .theta..sub.2 is not smaller than the upper limit of the
condition (2), i.e. 60.degree., the optical path extending through
the prism of the ocular optical system becomes excessively long,
resulting unfavorably in an increase in size of the prism. If
.theta..sub.2 is not larger than the lower limit of the condition
(2), i.e. 30.degree., because .theta..sub.2 is closely related to
.theta..sub.1, .theta..sub.1 becomes undesirably large, causing
aberration produced by the concave mirror 5 to become large and
impossible to correct by another surface satisfactorily.
It is more desirable that the internal reflection at the second
surface 4 should be total reflection. By tilting the second surface
4 such that total reflection takes place at the second surface 4,
it becomes unnecessary to provide reflection coating on the second
surface 4. If the second surface 4 is disposed so as to pass light
rays totally reflected by the first surface 3, it is unnecessary to
separate reflecting and transmitting regions from each other as is
the case with the first surface 3. Accordingly, the ocular optical
system can be reduced in size. In the case of total reflection, a
reflectivity of 100% can be obtained; in the case of reflection by
coating, only a reflectivity of about 90% can be obtained.
Next, the image display apparatus according to the second aspect of
the present invention will be explained. The image display
apparatus is characterized in that an area that is surrounded by
four optical surfaces is filled with a medium having a refractive
index larger than 1. In the image display apparatus according to
the first aspect of the present invention, light rays pass through
the second surface, which serves as both reflecting and
transmitting surfaces, before reaching the image display device,
whereas in the image display apparatus according to the second
aspect of the present invention, a fourth surface which serves as
only a transmitting surface is provided, thereby enabling even more
favorable aberration correction.
In this case also, it is desirable that internal reflection at the
first surface after reflection at the third should be total
reflection. It is also desirable to dispose the third surface such
that, after being reflected by the second surface, light rays on
the observer's visual axis are tilted at approximately 30.degree.
toward the observer's eyeball by reflection at the third surface.
It is preferable to satisfy the following condition:
where .theta..sub.1 is the tilt angle of the light rays.
It is even more desirable to restrict the range defined by the
condition (1) to the range defined by the following condition
(1'):
It is also desirable to satisfy the following condition:
where .theta..sub.2 is the angle between the first and second
surfaces 3 and 4.
In the decentered optical element (prism) in the image display
apparatus according to the second aspect of the present invention,
the second and third surfaces, together with the first surface as
it causes internal reflection, are reflecting surfaces. Therefore,
no chromatic aberration is produced at these surfaces.
Further, at the third or fourth surface, which lies in close
proximity to the image display device, principal rays are
approximately parallel to the optical axis. Therefore, the third or
fourth surface produces minimal lateral chromatic aberration.
Consequently, chromatic aberration in the ocular optical system is
produced by only the first surface, which is a refracting surface.
Thus, the chromatic aberration in the ocular optical system can be
substantially ignored. However, it is more desirable to correct
lateral chromatic aberration produced by the first surface, and it
is possible to display an image which is clearer and of higher
resolution by correcting the lateral chromatic aberration.
Accordingly, the ocular optical system is preferably arranged such
that a decentered optical element, together with at least one
optical surface having refracting action, is disposed between the
observer's eyeball and the image display device. By doing so,
optical elements constituting the ocular optical system can be
composed of two or more different mediums, and it becomes possible
to correct the lateral chromatic aberration by virtue of the
difference in Abbe's number between these mediums.
Chromatic aberration produced by the first surface can be corrected
by forming the above-described at least one optical surface from a
surface which produces chromatic aberration which is approximately
equal in quantity but opposite in sign to the chromatic aberration
produced by the first surface. That is, it is desirable to dispose
at least one optical boundary surface in the optical path of the
ocular optical system.
The correction of chromatic aberration will be explained below more
specifically. By disposing a decentered optical element, together
with at least one optical surface having refracting action, in the
optical path extending from the image display device to the
observer's eyeball, the ocular optical system can be composed of
two or more different mediums. In this case, lateral chromatic
aberration can be corrected by virtue of the Abbe's number
difference between the different mediums. Conditions for the
correction of lateral chromatic aberration, which are generally
known as achromatic conditions, are satisfied by appropriately
selecting Abbe's numbers v.sub.1 and v.sub.2.
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. That is,
the observer can see the observation image in his/her own easy
posture. For example, even a sick person who is bedridden can see
the observation image in a lying position with the image display
apparatus fitted to his/her head.
Further, it becomes possible for the observer to see the
observation image with both eyes without fatigue by providing a
device for supporting at least two image display apparatuses at a
predetermined spacing. Further, if images with a disparity
therebetween are displayed on the image display areas of the right
and left image display devices, and these images are observed with
both eyes, it is possible to enjoy viewing a stereoscopic
image.
Further, if an ocular optical system 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 optical system can be used as an
imaging optical system, e.g. a finder optical system of a camera,
as shown in FIGS. 9 and 10.
Still 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 image
display apparatus according to the present invention.
FIG. 2 illustrates an optical ray trace of Example 2 of an image
display apparatus according to the present invention.
FIG. 3 illustrates an optical ray trace of Example 3 of an image
display apparatus according to the present invention.
FIG. 4 illustrates an optical ray trace of Example 4 of an image
display apparatus according to the present invention.
FIG. 5 illustrates an optical ray trace of Example 5 of an image
display apparatus according to the present invention.
FIG. 6 illustrates an optical ray trace of Example 6 of an image
display apparatus according to the present invention.
FIG. 7 illustrates an optical ray trace of Example 7 of an image
display apparatus according to the present invention.
FIGS. 8(a) and 8(b) are sectional and perspective views showing one
example of an image display apparatus according to the present
invention which is arranged as a head-mounted image display
apparatus.
FIG. 9 is a perspective view of a compact camera in which an ocular
optical system of an image display apparatus according to the
present invention is used as an imaging optical system.
FIG. 10 shows an arrangement in a case where an ocular optical
system of an image display apparatus according to the present
invention is used as an imaging optical system.
FIGS. 11(a) and 11(b) are conceptual views showing optical paths in
an image display apparatus according to the present invention.
FIG. 12 is a view for explanation of the meaning of the condition
(1) in the present invention.
FIGS. 13(a) and 13(b) show an optical system of a conventional
image display apparatus.
FIG. 14 shows an optical system of another conventional image
display apparatus.
FIGS. 15(a) and 15(b) show an optical system of still another
conventional image display apparatus.
FIG. 16 shows an optical system of a further conventional image
display apparatus.
FIG. 17 shows an optical system of a still further conventional
image display apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples 1 to 7 of the image display apparatus according to the
present invention will be described below with reference to FIGS. 1
to 7, which are sectional views of image display apparatuses
designed for a single eye according to Examples 1 to 7.
Constituent parameters in Examples 1 to 5 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 7. 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 Z-axis, where the direction toward an ocular optical
system 8 from the origin is defined as 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
Y-axis, where the upward direction is defined as position
direction. Further, the horizontal direction (as viewed from the
observer's eyeball) which perpendicularly intersects the observer's
visual axis 2 is taken as X-axis, where the leftward direction is
defined as positive direction. That is, the plane of the figure is
defined as YZ-plane, and a plane which is perpendicular to the
plane of the figure is defined as XZ-plane. Further, it is assumed
that the optical axis is bent in the YZ-plane, which is parallel to
the plane of the figure.
In the constituent parameters (shown later), the surface No. 2 is
given a surface separation, which is the distance from the surface
No. 1 along the Z-axis, and a point on the surface No. 2 that lies
on the Z-axis is defined as a reference point for the surface No. 2
and the surfaces following it. The surface No. 2 and the surfaces
following it are each given eccentricities Y and Z and a tilt angle
.theta.. The eccentricity Y is a distance by which the vertex of
each particular surface decenters in the Y-axis direction from the
reference point. The eccentricity Z is a distance by which the
vertex of each particular surface decenters in the Z-axis direction
from the reference point. The tilt angle .theta. is an inclination
angle of the center axis of each particular surface relative to the
Z-axis. Regarding the tilt angle .theta., it is positive when the
rotation is counterclockwise. It should be noted that the surface
of the image display device 7 is also given eccentricities Y and Z
and a tilt angle .theta.. In the case of the image display device
7, the eccentricity Y is a distance by which the center of the
display surface decenters in the Y-axis direction from the center
of the surface No. 1 (i.e. the observer's pupil position 1), and
the eccentricity Z is a distance by which the center of the display
surface decenters in the Z-axis direction from the center of the
surface No. 1. The tilt angle .theta. is an inclination angle of a
line normal to the display surface relative to the Z-axis.
Regarding the surface separation, the direction of backward ray
tracing along the optical axis is defined as positive
direction.
The non-rotationally symmetric aspherical configuration of each
surface may be expressed in the coordinate system defining the
surface as follows: ##EQU1##
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.
The rotationally symmetric aspherical configuration of each surface
may be expressed by.
where R is the paraxial curvature radius; K is the conical
coefficient; A and B are 4th- and 6th-order aspherical
coefficients, respectively; and h is given by h.sup.2 =X.sup.2
+y.sup.2.
It should be noted that the refractive index of the medium between
a pair of adjacent surfaces is expressed by the refractive index
for the spectral d-line. Lengths are given in millimeters.
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 bent by the ocular optical system may be any of the
upward, downward and sideward directions of the observer.
In each sectional view, reference numeral 1 denotes an observer's
pupil position, 2 an observer's visual axis, 3 a first surface of
an ocular optical system, 4 a second surface of the ocular optical
system, 5 a third surface of the ocular optical system, 6 a fourth
surface of the ocular optical system, 7 an image display device, 8
an ocular optical system, and 9 an optical surface.
The actual path of light rays in each example is as follows: In
Example 1, for instance, a bundle of light rays emitted from the
image display device 7 enters the ocular optical system 8 while
being refracted by the second surface 4 of the ocular optical
system 8 and is internally reflected by the first surface 3 and
then reflected by the third surface 5. Then, the ray bundle is
reflected by the second surface 4 again and then refracted by the
first surface 3 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.
EXAMPLE 1
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 1, the horizontal field angle is 30.degree., while the
vertical field angle is 22.7.degree., and the pupil diameter is 8
millimeters. In the constituent parameters (shown later), the first
surface 3 (surface Nos. 2 and 5), the second surface 4 (surface
Nos. 3 and 6), and the third surface 5 (surface No. 4) are all
spherical surfaces.
EXAMPLE 2
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 2, the horizontal field angle is 30.degree., while the
vertical field angle is 22.7.degree., and the pupil diameter is 8
millimeters. In the constituent parameters (shown later), the first
surface 3 (surface Nos. 2 and 5) and the second surface 4 (surface
Nos. 3 and 6) are spherical surfaces, and the third surface 5
(surface No. 4) is an anamorphic aspherical surface.
EXAMPLE 3
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 3, the horizontal field angle 30.degree., while the
vertical field angle is 22.7.degree., and the pupil diameter is 8
millimeters. In the constituent parameters (shown later), the first
surface 3 (surface Nos. 2 and 5) and the third surface 5 (surface
No. 4) are anamorphic aspherical surfaces, and the second surface 4
(surface Nos. 3 and 6) is a spherical surface.
EXAMPLE 4
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 4, the horizontal field angle is 30.degree., while the
vertical field angle is 22.7.degree., and the pupil diameter is 8
millimeters. In the constituent parameters (shown later), the first
surface 3 (surface Nos. 2 and 5), the second surface 4 (surfaces
Nos. 3 and 6), and the third surface 5 (surface No. 4) are all
spherical surfaces.
EXAMPLE 5
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 5, the horizontal field angle is 45.degree., while the
vertical field angle is 34.52.degree., and the pupil diameter is 8
millimeters. In the constituent parameters (shown later), the first
surface 3 (surface Nos. 2 and 5) and the second surface 4 (surfaces
Nos. 3 and 6) are spherical surfaces, and the third surface 5
(surface No. 4) is an anamorphic aspherical surface.
EXAMPLE 6
This example relates to an image display apparatus according to the
second aspect of the present invention. As shown in the sectional
view of FIG. 6, an optical boundary surface 9 is disposed on the
entrance side of the fourth surface 6 of the ocular optical system
8, thereby correcting lateral chromatic aberration. Description of
constituent parameters in this example is omitted.
EXAMPLE 7
This example relates to an image display apparatus according to the
first aspect of the present invention. As shown in the sectional
view of FIG. 7, an optical boundary surface 9 is disposed on the
entrance-exit side of the third surface 5 of the ocular optical
system 8, thereby correcting lateral chromatic aberration.
Description of constituent parameters in this example is
omitted.
Constituent parameters in the above-described Examples 1 to 5 are
as follows:
Radius Refractive Surface of Surface index Abbe's No. No. curvature
separation (Eccentricity) (Tilt angle) 1 .infin. 29.409 (pupil) 2
-1065.772 1.51633 64.10 Y -32.663 .theta. 7.273.degree. Z 0.277 3
4956.938 1.51633 64.10 Y 17.403 .theta. 53.107.degree. Z -13.120 4
133.057 1.51633 64.10 Y -44.740 .theta. 98.811.degree. Z -30.773 5
-1065.772 1.51633 64.10 Y -32.663 .theta. 7.273.degree. Z 0.277 6
4956.938 Y 17.043 .theta. 53.107.degree. Z -13.120 7 (display Y
23.253 .theta. 81.241.degree. device) Z 44.479
.sup.(1).theta..sub.1 = 32.degree. .sup.(2).theta..sub.2 =
45.degree.
Radius Refractive Surface of Surface index Abbe's No. No. curvature
separation (Eccentricity) (Tilt angle) 1 .infin. 29.409 (pupil) 2
-1065.772 1.51633 64.10 Y -32.663 .theta. 7.273.degree. Z 0.277 3
4956.938 1.51633 64.10 Y 17.403 .theta. 53.107.degree. Z -13.120 4
133.057 1.51633 64.10 Y -44.740 .theta. 98.811.degree. Z -30.773 5
-1065.772 1.51633 64.10 Y -32.663 .theta. 7.273.degree. Z 0.277 6
4956.938 Y 17.043 .theta. 53.107.degree. Z -13.120 7 (display Y
23.253 .theta. 81.241.degree. device) Z 44.479
.sup.(1).theta..sub.1 = 32.degree. .sup.(2).theta..sub.2 =
45.degree.
Radius Refractive Surface of Surface index Abbe's No. No. curvature
separation (Eccentricity) (Tilt angle) 1 .infin. 24.480 (pupil) 2
R.sub.y -736.361 1.48700 70.40 R.sub.x -505.846 Y -21.744 .theta.
-2.450.degree. K.sub.y 0.000000 Z 0.000 K.sub.x 0.000000 AR
-0.306697 .times. 10.sup.-7 BR -0.809687 .times. 10.sup.-10 AP
0.263980 .times. 10.sup.-1 BP 0.574278 .times. 10.sup.-1 3 -553.259
1.48700 70.40 Y 23.482 .theta. 53.267.degree. Z -4.568 4 R.sub.y
146.168 1.48700 70.40 R.sub.x 128.931 Y -42.800 .theta.
93.371.degree. K.sub.y -0.06771 Z -31.014 K.sub.x -0.407545 AR
0.550524 .times. 10.sup.-8 BR -0.151433 .times. 10.sup.-11 AP
-0.155988 .times. 10.sup.-1 BP 0.437690 5 R.sub.y -736.361 1.48700
70.40 R.sub.x -505.846 Y -21.744 .theta. -2.450.degree. K.sub.y
0.000000 Z 0.000 K.sub.x 0.000000 AR -0.306697 .times. 10.sup.-7 BR
0.809687 .times. 10.sup.-10 AP 0.263980 .times. 10.sup.1 BP
0.574278 .times. 10.sup.-1 6 -553.259 Y 23.482 .theta.
53.267.degree. Z -4.568 7 (display Y 16.438 .theta. 58.428.degree.
device) Z 39.101 .sup.(1).theta..sub.1 = 36.degree.
.sup.(2).theta..sub.2 = 50.degree.
Radius Refractive Surface of Surface index Abbe's No. No. curvature
separation (Eccentricity) (Tilt angle) 1 .infin. 32.764 (pupil) 2
-677.269 1.51633 64.10 Y -57.272 .theta. 8.459.degree. Z 3.506 3
2651.719 1.51633 64.10 Y 13.829 .theta. 53.626.degree. Z 5.278 4
137.501 1.51633 64.10 Y -41.948 .theta. 101.521.degree. Z -17.362 5
-677.269 1.51633 64.10 Y -57.272 .theta. 8.459.degree. Z 3.506 6
2651.719 Y 13.829 .theta. 53.626.degree. Z 5.278 7 (display Y
31.172 .theta. 88.536.degree. device) Z 31.427
.sup.(1).theta..sub.1 = 32.degree. .sup.(2).theta..sub.2 =
40.degree.
Radius Refractive Surface of Surface index Abbe's No. No. curvature
separation (Eccentricity) (Tilt angle) 1 .infin. 32.764 (pupil) 2
-677.269 1.51633 64.10 Y -57.272 .theta. 8.459.degree. Z 3.506 3
2651.719 1.51633 64.10 Y 13.829 .theta. 53.626.degree. Z 5.278 4
137.501 1.51633 64.10 Y -41.948 .theta. 101.521.degree. Z -17.362 5
-677.269 1.51633 64.10 Y -57.272 .theta. 8.459.degree. Z 3.506 6
2651.719 Y 13.829 .theta. 53.626.degree. Z 5.278 7 (display Y
31.172 .theta. 88.536.degree. device) Z 31.427
.sup.(1).theta..sub.1 = 32.degree. .sup.(2).theta..sub.2 =
40.degree.
Although examples of the image display apparatus according to the
present invention have been described above, it should be noted
that the present invention is not necessarily limited to these
examples, and that various modifications may be imparted thereto.
To arrange the image display apparatus according to the present
invention as a head-mounted image display apparatus (HMD) 11, as
shown in the sectional view of FIG. 8(a) and the perspective view
of FIG. 8(b), the HMD 11 is fitted to the observer's head by using
a headband 12, for example, which is attached to the HMD 15.
Further, the ocular optical system 8 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. 9, the ocular optical system 8 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. 10 shows the
arrangement of an optical system in a case where an 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.t. An image that is formed by the
objective optical system L.sub.t can be observed through an ocular
lens O.sub.c.
Although in some examples an anamorphic aspherical surface is used
as a surface configuration from the viewpoint of optical design,
surface configurations usable in the present invention are not
necessarily limited to those defined by the above-described
expressions. It will be apparent that the object of the present
invention can be attained by adopting the arrangement of the
present invention even in the case of other surfaces, e.g. a
three-dimensional surface (free-form surface), a toric surface,
etc.
As will be clear from the foregoing description, the present
invention makes it possible to provide an image display apparatus
which has a wide field angle and is extremely small in size and
light in weight.
* * * * *