U.S. patent application number 09/935633 was filed with the patent office on 2002-05-23 for optical path splitting element and image display apparatus using the same.
Invention is credited to Togino, Takayoshi.
Application Number | 20020060852 09/935633 |
Document ID | / |
Family ID | 18743066 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020060852 |
Kind Code |
A1 |
Togino, Takayoshi |
May 23, 2002 |
Optical path splitting element and image display apparatus using
the same
Abstract
An optical path splitting element for splitting a light beam
from a single object into two optical paths (left and right) is
made compact in size and given a power to reduce the number of
components thereof. An image display apparatus uses the optical
path splitting element. The left and right optical paths are not in
plane symmetry with each other but in 180-degree rotational
symmetry with respect to only a straight line passing through the
center of the object. When a pair of reflecting surfaces (left and
right) closest to the object side are defined as first reflecting
surfaces and a pair of reflecting surfaces (left and right) closest
to the exit side are defined as final reflecting surfaces, axial
principal rays incident on the first reflecting surfaces and those
exiting from the final reflecting surfaces are not coplanar with
each other in either of the left and right optical paths. At least
one pair of the reflecting surface pairs are formed from
rotationally asymmetric curved reflecting surfaces having the
function of correcting decentration aberrations.
Inventors: |
Togino, Takayoshi; (Tokyo,
JP) |
Correspondence
Address: |
PILLSBURY WINTHROP LLP
1600 TYSONS BOULEVARD
MCLEAN
VA
22102
US
|
Family ID: |
18743066 |
Appl. No.: |
09/935633 |
Filed: |
August 24, 2001 |
Current U.S.
Class: |
359/639 ;
359/636; 359/638; 359/640 |
Current CPC
Class: |
G02B 2027/0136 20130101;
G02B 2027/0132 20130101; G02B 2027/0178 20130101; G02B 27/0172
20130101 |
Class at
Publication: |
359/639 ;
359/638; 359/640; 359/636 |
International
Class: |
G02B 027/14; G02B
027/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2000 |
JP |
2000-254052 |
Claims
What we claim is:
1. An optical path splitting element for splitting a light beam
from a single object into two optical paths, wherein the optical
paths in said optical path splitting element are not in plane
symmetry with each other but in 180-degree rotational symmetry with
respect to only a straight line passing through a center of the
object, said optical path splitting element having at least two
pairs of reflecting surfaces in said optical paths, wherein when a
pair of reflecting surfaces closest to an object side of said
optical path splitting element among said at least two pairs of
reflecting surfaces are defined as a left first reflecting surface
and a right first reflecting surface, respectively, and a pair of
reflecting surfaces closest to an exit side of said optical path
splitting element among said at least two pairs of reflecting
surfaces are defined as a left final reflecting surface and a right
final reflecting surface, respectively, the optical paths in said
optical path splitting element are arranged so that an entering
optical axis of an axial principal ray incident on the left first
reflecting surface and an exiting optical axis of the axial
principal ray exiting from the left final reflecting surface are
not coplanar with each other, and an entering optical axis of an
axial principal ray incident on the right first reflecting surface
and an exiting optical axis of the axial principal ray exiting from
the right final reflecting surface are not coplanar with each
other, and wherein at least one pair of said at least two pairs of
reflecting surfaces are formed from rotationally asymmetric curved
reflecting surfaces having a function of correcting decentration
aberrations.
2. An optical path splitting element according to claim 1, wherein
said at least two pairs of reflecting surfaces are arranged so that
optical axes exiting said optical path splitting element extend in
approximately a same direction.
3. An optical path splitting element according to claim 2, wherein
said at least two pairs of reflecting surfaces are arranged so that
the optical axes exiting said optical path splitting element are
approximately parallel to each other.
4. An optical path splitting element according to claim 1, which
has at least three pairs of reflecting surfaces, wherein said at
least three pairs of reflecting surfaces are formed from
rotationally asymmetric curved reflecting surfaces having a
function of correcting decentration aberrations.
5. An optical path splitting element according to claim 1, which
comprises a prism member, wherein all of said at least two pairs of
reflecting surfaces are back-coated reflecting surfaces formed on
surfaces of said prism member.
6. An optical path splitting element according to claim 1, which is
used as at least a part of a viewing optical system, wherein an
image display device is placed at a position of said object.
7. An image display apparatus comprising: an optical path splitting
element for splitting a light beam from a single object into two
optical paths, wherein the optical paths in said optical path
splitting element are not in plane symmetry with each other but in
180-degree rotational symmetry with respect to only a straight line
passing through a center of the object, said optical path splitting
element having at least two pairs of reflecting surfaces in said
optical paths, wherein when a pair of reflecting surfaces closest
to an object side of said optical path splitting element among said
at least two pairs of reflecting surfaces are defined as a left
first reflecting surface and a right first reflecting surface,
respectively, and a pair of reflecting surfaces closest to an exit
side of said optical path splitting element among said at least two
pairs of reflecting surfaces are defined as a left final reflecting
surface and a right final reflecting surface, respectively, the
optical paths in said optical path splitting element are arranged
so that an entering optical axis of an axial principal ray incident
on the left first reflecting surface and an exiting optical axis of
the axial principal ray exiting from the left final reflecting
surface are not coplanar with each other, and an entering optical
axis of an axial principal ray incident on the right first
reflecting surface and an exiting optical axis of the axial
principal ray exiting from the right final reflecting surface are
not coplanar with each other, and wherein at least one pair of said
at least two pairs of reflecting surfaces are formed from
rotationally asymmetric curved reflecting surfaces having a
function of correcting decentration aberrations; and an image
display device placed at a position of said object; wherein left
and right eyeballs of an observer are placed at left and right exit
pupils formed in left and right optical paths exiting said optical
path splitting element, thereby allowing observation of an image
displayed by said image display device.
8. An image display apparatus according to claim 7, wherein said
optical path splitting element is formed from a prism member, said
prism member having: an entrance surface through which a display
light beam from said image display device enters said prism member
so as to be incident on said left first reflecting surface and said
right first reflecting surface; a left exit surface through which a
light beam reflected from said left final reflecting surface exits
said prism member; and a right exit surface through which a light
beam reflected from said right final reflecting surface exits said
prism member; wherein said left first reflecting surface and said
right first reflecting surface are positioned to face both said
image display device and said entrance surface.
9. An image display apparatus according to claim 8, wherein an
anti-reflection member is provided for an area including a boundary
portion between said left first reflecting surface and said right
first reflecting surface to prevent light rays emitted
perpendicularly from a central region of said image display device
from being reflected as ghost light.
10. An image display apparatus according to claim 7, wherein said
optical path splitting element forms an intermediate image of the
image displayed by said image display device in each of said left
and right optical paths.
11. An image display apparatus according to claim 7, wherein said
image display device is rotated through a desired angle about the
straight line passing through the center of said object as an axis
of rotation so that a horizontal direction of an image display area
of said image display device is at an angle to a plane containing
the left and right optical paths exiting said optical path
splitting element.
12. An image display apparatus according to claim 7, wherein the
following condition is
satisfied:10.degree.<.theta.<150.degree. (1)where .theta. is
an angle formed between axial principal rays of left and right
light beams led from each pixel located at least in a central
portion of said image display device to the left and right eyeballs
of the observer.
13. An optical path combining element using said optical path
splitting element according to claim 1 to combine together light
rays in two optical paths.
14. An image pickup apparatus comprising: said image display
apparatus according to claim 7; and an image pickup device provided
in place of said image display device; wherein said exit pupils are
arranged as entrance pupils through which a light beam from a
subject passes, and a subject image is formed on said image pickup
device.
15. A projection apparatus comprising: said image display apparatus
according to claim 7; a projection object provided in place of said
image display device; and a screen placed in front of said exit
pupils to form a projected image of said projection object on said
screen.
Description
[0001] This application claims benefit of Japanese Application No.
2000-254052 filed in Japan on Aug. 24, 2000, the contents of which
are incorporated by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical path splitting
element and an image display apparatus using the same. More
particularly, the present invention relates to an optical path
splitting element for splitting a light beam from a single object
into two optical paths. The present invention also relates to a
head- or face-mounted image display apparatus using such an optical
path splitting element.
[0004] 2. Discussion of Related Art
[0005] There has heretofore been known an optical path splitting
element for leading an image displayed by a single display device
to both eyes of an observer, as disclosed in Japanese Patent
Application Unexamined Publication No. [hereinafter referred to as
"JP(A)"]9- 181999. This splitting element uses a single prism to
split a light beam from the displayed image into two optical paths
extending in different directions.
[0006] In an image display apparatus using the above-described
splitting element, however, when the image display device is
reduced in size, it is necessary to shorten the focal length of the
optical system while ensuring the required eye relief. Therefore,
it is difficult to construct a viewing optical system of wide field
angle.
[0007] There has also been proposed an image display device using a
half-mirror to split an optical path as disclosed in JP(A)
9-061748.
[0008] In the above-described conventional optical path splitting
element that splits the light beam into two optical paths extending
in different directions, the size of the optical path splitting
element becomes unfavorably large. Accordingly, an image display
apparatus using the optical path splitting element becomes
undesirably large in size and heavy in weight. The above-described
conventional method of splitting an optical path by using a
half-mirror suffers from the problem that because the light
quantity is halved for each optical path, the image for observation
becomes dark.
SUMMARY OF THE INVENTION
[0009] The present invention was made in view of the
above-described problems with the prior art.
[0010] Accordingly, an object of the present invention is to
provide a compact optical path splitting element having a reduced
number of components and also provide an image display apparatus
using the optical path splitting element. More specifically, the
present invention provides an optical path splitting element having
at least two split axial principal rays each extending from the
center of an object to the center of an image. The optical path
splitting element uses a three-dimensional optical system in which
bent segments forming each of the axial principal rays lie in at
least two planes, thereby making the optical path splitting element
compact in size. At the same time, a power is given to the optical
path splitting element to reduce the number of components
thereof.
[0011] To attain the above-described object, the present invention
provides an optical path splitting element for splitting a light
beam from a single object into two optical paths. The optical paths
in the optical path splitting element are not in plane symmetry
with each other but in 180-degree rotational symmetry with respect
to only a straight line passing through the center of the object.
The optical path splitting element has at least two pairs of
reflecting surfaces in the optical paths. When a pair of reflecting
surfaces closest to the object side of the optical path splitting
element among the at least two pairs of reflecting surfaces are
defined as a left first reflecting surface and a right first
reflecting surface, respectively, and a pair of reflecting surfaces
closest to the exit side of the optical path splitting element
among the at least two pairs of reflecting surfaces are defined as
a left final reflecting surface and a right final reflecting
surface, respectively, the optical paths in the optical path
splitting element are arranged so that the entering optical axis of
an axial principal ray incident on the left first reflecting
surface and the exiting optical axis of the axial principal ray
exiting from the left final reflecting surface are not coplanar
with each other, and the entering optical axis of an axial
principal ray incident on the right first reflecting surface and
the exiting optical axis of the axial principal ray exiting from
the right final reflecting surface are not coplanar with each
other. At least one pair of the at least two pairs of reflecting
surfaces are formed from rotationally asymmetric curved reflecting
surfaces having the function of correcting decentration
aberrations.
[0012] In addition, the present invention provides an image display
apparatus including an optical path splitting element for splitting
a light beam from a single object into two optical paths. The
optical paths in the optical path splitting element are not in
plane symmetry with each other but in 180-degree rotational
symmetry with respect to only a straight line passing through the
center of the object. The optical path splitting element has at
least two pairs of reflecting surfaces in the optical paths. When a
pair of reflecting surfaces closest to the object side of the
optical path splitting element among the at least two pairs of
reflecting surfaces are defined as a left first reflecting surface
and a right first reflecting surface, respectively, and a pair of
reflecting surfaces closest to the exit side of the optical path
splitting element among the at least two pairs of reflecting
surfaces are defined as a left final reflecting surface and a right
final reflecting surface, respectively, the optical paths in the
optical path splitting element are arranged so that the entering
optical axis of an axial principal ray incident on the left first
reflecting surface and the exiting optical axis of the axial
principal ray exiting from the left final reflecting surface are
not coplanar with each other, and the entering optical axis of an
axial principal ray incident on the right first reflecting surface
and the exiting optical axis of the axial principal ray exiting
from the right final reflecting surface are not coplanar with each
other. At least one pair of the at least two pairs of reflecting
surfaces are formed from rotationally asymmetric curved reflecting
surfaces having the function of correcting decentration
aberrations. The image display apparatus further includes an image
display device placed at the position of the object. The left and
right eyeballs of an observer are placed at left and right exit
pupils formed in the left and right optical paths exiting the
optical path splitting element, thereby allowing observation of an
image displayed by the image display device.
[0013] The reasons for adopting the above-described arrangements in
the present invention, together with the functions thereof, will be
described below.
[0014] FIG. 1 is a perspective view schematically showing the
surfaces and optical axes of a viewing optical system of an image
display apparatus according to Example 1 (described later) . The
viewing optical system includes an optical path splitting element
10 and a pair of ocular optical systems 20L and 20R (left and
right). The optical path splitting element 10 is formed from a
decentered prism. The viewing optical system has a single image
display device 1 common to left and right optical systems. A
display light beam from the image display device 1 is split into
left and right beams through the optical path splitting element 10.
The beams are passed through the left and right ocular optical
systems 20L and 20R to project enlarged images of the image display
device 1 into the left and right eyeballs of an observer. In
Example 1, the optical path splitting element 10 has a first
surface 11 as a common entrance surface (refracting surface)
through which left and right axial principal rays 2L and 2R
emanating from the image display device 1 at an angle to each other
enter the optical path splitting element 10. Regarding the left
optical path, the optical path splitting element 10 has a second
surface 12L, a third surface 13L, a fourth surface 14L, and a fifth
surface 15L. The second surface 12L reflects the left axial
principal ray 2L entering through the first surface 11. The third
surface 13L reflects the left axial principal ray 2L reflected from
the second surface 12L. The fourth surface 14L reflects the left
axial principal ray 2L reflected from the third surface 13L. The
fifth surface 15L is an exit surface (refracting surface) through
which the left axial principal ray 2L reflected from the fourth
surface 14L exits the optical path splitting element 10 so as to
enter the left ocular optical system 20L. Regarding the right
optical path, the optical path splitting element 10 has a second
surface 12R, a third surface 13R, a fourth surface 14R, and a fifth
surface 15R. The second surface 12R reflects the right axial
principal ray 2R entering through the first surface 11. The third
surface 13R reflects the right axial principal ray 2R reflected
from the second surface 12R. The fourth surface 14R reflects the
right axial principal ray 2R reflected from the third surface 13R.
The fifth surface 15R is an exit surface (refracting surface)
through which the right axial principal ray 2R reflected from the
fourth surface 14R exits the optical path splitting element 10 so
as to enter the right ocular optical system 20R. The left and right
reflecting surfaces 12L to 14L and 12R to 14R are formed from
back-coated mirrors.
[0015] The surface configurations of the above-described surfaces,
i.e. from the first surface 11 to the left and right exit surfaces
15L and 15R, are determined so that the configurations of the left
and right axial principal rays 2L and 2R emanating from the image
display device 1 in the object plane and exiting from the left and
right fifth surfaces 15L and 15R as exit surfaces are in 180-degree
rotational symmetry with respect to a straight line A-A' passing
through the center of the display surface of the image display
device 1 at approximately right angles to the display surface. To
form left and right optical paths that are in 180-degree rotational
symmetry with each other as stated above, the optical path
splitting element 10, which is a decentered prism, should be
constructed by arranging the first surface 11, the second surfaces
12R and 12L, the third surfaces 13R and 13L, the fourth surfaces
14R and 14L, and the fifth surfaces 15R and 15L so that when an
optical system for the right optical path formed from the first
surface 11, the second surface 12R, the third surface 13R, the
fourth surface 14R and the fifth surface 15R is rotated through 180
degrees about the straight line A-A', these surfaces are coincident
with the first surface 11, the second surface 12L, the third
surface 13L, the fourth surface 14L and the fifth surface 15L,
which form an optical system for the left optical path. In this
case, the axial principal ray 2R (2L) extending from the first
surface 11 to the fifth surface 15R (15L) passes along a
three-dimensionally decentered optical path. Therefore, it is
necessary to select a surface configuration and arrangement for
each surface so that the entering optical axis of the axial
principal ray 2R (2L) incident on the second surface 12R (12L) as a
first reflecting surface and the exiting optical axis of the axial
principal ray 2R (2L) exiting from the fourth surface 14R (14L) as
the final reflecting surface are not coplanar with each other.
[0016] To allow the optical path splitting element 10 to be used as
a part of a viewing optical system for distributing an image
displayed by the single image display device 1 to the left and
right eyeballs of an observer, it is necessary to select a surface
configuration and arrangement for each surface of the optical path
splitting element 10 so that the left and right optical axes, which
are coincident with the left and right axial principal rays 2L and
2R emerging from the left and right exit surfaces (refracting
surfaces) 15L and 15R, are approximately parallel to each other so
as to extend in approximately the same direction.
[0017] In the optical path splitting element 10 according to the
present invention, it is desirable that at least one of the left
and right reflecting surface pairs, i.e. the second surfaces 12R
and 12L, the third surfaces 13R and 13L, and the fourth surfaces
14R and 14L, should be formed from rotationally asymmetric curved
reflecting surfaces having the function of correcting decentration
aberrations.
[0018] In the optical path splitting element 10 according to the
present invention, three-dimensionally decentered optical paths are
formed, as has been stated above. Consequently, the reflecting
surfaces are decentered. Moreover, if an optical power is given to
such a decentered reflecting surface, decentration aberrations
occur. To correct the decentration aberrations, the optical path
splitting element 10 needs to have at least one pair of reflecting
surfaces having a rotationally asymmetric curved surface
configuration.
[0019] In the present invention, a free-form surface is used as a
typical example of a surface having a rotationally asymmetric
curved surface configuration. A free-form surface is defined by the
following equation. The Z-axis of the defining equation is the axis
of a free-form surface. 1 Z = cr 2 / [ 1 + { 1 - ( 1 + k ) c 2 r 2
} ] + j = 2 66 C j X m Y n ( a )
[0020] In the equation (a), the first term is a spherical surface
term, and the second term is a free-form surface term.
[0021] In the spherical surface term:
[0022] c: the curvature at the vertex
[0023] k: a conic constant
[0024] r={square root}{square root over ( )}(X.sup.2+Y.sup.2)
[0025] The free-form surface term is given by 2 j = 2 66 C j X m Y
n = C 2 X + C 3 Y + C 4 X 2 + C 5 XY + C 6 Y 2 + C 7 X 3 + C 8 X 2
Y + C 9 XY 2 + C 10 Y 3 + C 11 X 4 + C 12 X 3 Y + C 13 X 2 Y 2 + C
14 XY 3 + C 15 Y 4 + C 16 X 5 + C 17 X 4 Y + C 18 X 3 Y 2 + C 19 X
2 Y 3 + C 20 XY 4 + C 21 Y 5 + C 22 X 6 + C 23 X 5 Y + C 24 X 4 Y 2
+ C 25 X 3 Y 3 + C 26 X 2 Y 4 + C 27 XY 5 + C 28 Y 6 + C 29 X 7 + C
30 X 6 Y + C 31 X 5 Y 2 + C 32 X 4 Y 3 + C 33 X 3 Y 4 + C 34 X 2 Y
5 + C 35 XY 6 + C 36 Y 7
[0026] where C.sub.j (j is an integer of 2 or higher) are
coefficients.
[0027] In general, the above-described free-form surface does not
have planes of symmetry in both the XZ- and YZ-planes. However, a
free-form surface having only one plane of symmetry parallel to the
YZ-plane is obtained by making all terms of odd-numbered degrees
with respect to X zero. A free-form surface having only one plane
of symmetry parallel to the XZ-plane is obtained by making all
terms of odd-numbered degrees with respect to Y zero.
[0028] In addition, free-form surfaces as the above-described
surfaces with a rotationally asymmetric curved surface
configuration may be defined by Zernike polynomials. That is, the
configuration of a free-form surface may be defined by the
following equation (b). The Z-axis of the defining equation (b) is
the axis of Zernike polynomial. A rotationally asymmetric surface
is defined by polar coordinates of the height of the Z-axis with
respect to the XY-plane. In the equation (b), R is the distance
from the Z-axis in the XY-plane, and A is the azimuth angle about
the Z-axis, which is expressed by the angle of rotation measured
from the X-axis. 3 x = R .times. cos ( A ) y = R .times. sin ( A )
Z = D 2 + D 3 R cos ( A ) + D 4 R sin ( A ) + D 5 R 2 cos ( 2 A ) +
D 6 ( R 2 - 1 ) + D 7 R 2 sin ( 2 A ) + D 8 R 3 cos ( 3 A ) + D 9 (
3 R 3 - 2 R ) cos ( A ) + D 10 ( 3 R 3 - 2 R ) sin ( A ) + D 11 R 3
sin ( 3 A ) + D 12 R 4 cos ( 4 A ) + D 13 ( 4 R 4 - 3 R 2 ) cos ( 2
A ) + D 14 ( 6 R 4 - 6 R 2 + 1 ) + D 15 ( 4 R 4 - 3 R 2 ) sin ( 2 A
) + D 16 R 4 sin ( 4 A ) + D 17 R 5 cos ( 5 A ) + D 18 ( 5 R 5 - 4
R 3 ) cos ( 3 A ) + D 19 ( 10 R 5 - 12 R 3 + 3 R ) cos ( A ) + D 20
( 10 R 5 - 12 R 3 + 3 R ) sin ( A ) + D 21 ( 5 R 5 - 4 R 3 ) sin (
3 A ) + D 22 R 5 sin ( 5 A ) + D 23 R 6 cos ( 6 A ) + D 24 ( 6 R 6
- 5 R 4 ) cos ( 4 A ) + D 25 ( 15 R 6 - 20 R 4 + 6 R 2 ) cos ( 2 A
) + D 26 ( 20 R 6 - 30 R 4 + 12 R 2 - 1 ) + D 27 ( 15 R 6 - 20 R 4
+ 6 R 2 ) sin ( 2 A ) + D 28 ( 6 R 6 - 5 R 4 ) sin ( 4 A ) + D 29 R
6 sin ( 6 A ) ( b )
[0029] where D.sub.m (m is an integer of 2 or higher) are
coefficients.
[0030] It should be noted that to design an optical system
symmetric with respect to the X-axis direction, D.sub.4, D.sub.5,
D.sub.6, D.sub.10, D.sub.11, D.sub.12, D.sub.13, D.sub.14,
D.sub.20, D.sub.21, D.sub.22 . . . should be used.
[0031] The above defining equations are shown to exemplify surfaces
with a rotationally asymmetric curved surface configuration.
Therefore, the same advantageous effects can be obtained for any
other defining equation that expresses such a rotationally
asymmetric curved surface configuration.
[0032] It should be noted that other examples of defining equations
for free-form surfaces include the following defining equation
(c):
Z=.SIGMA..SIGMA.C.sub.nmXY
[0033] Assuming that k=7 (polynomial of degree 7), for example, a
free-form surface is expressed by an expanded form of the above
equation as follows: 4 Z = C 2 + C 3 Y + C 4 X + C 5 Y 2 + C 6 Y X
+ C 7 X 2 + C 8 Y 3 + C 9 Y 2 X + C 10 YX 2 + C 11 X 3 + C 12 Y 4 +
C 13 Y 3 X + C 14 Y 2 X 2 + C 15 Y X 3 + C 16 X 4 + C 17 Y 5 + C 18
Y 4 X + C 19 Y 3 X 2 + C 20 Y 2 X 3 + C 21 YX 4 + C 22 X 5 + C 23 Y
6 + C 24 Y 5 X + C 25 Y 4 X 2 + C 26 Y 3 X 3 + C 27 Y 2 X 4 + C 28
Y X 5 + C 29 X 6 + C 30 Y 7 + C 31 Y 6 X + C 32 Y 5 X 2 + C 33 Y 4
X 3 + C 34 Y 3 X 4 + C 35 Y 2 X 5 + C 36 YX 6 + C 37 X 7 ( c )
[0034] It should be noted that an anamorphic surface or a toric
surface is also usable as a surface having a rotationally
asymmetric curved surface configuration.
[0035] It should be noted that the optical path splitting element
10 according to the present invention can have at least three pairs
of reflecting surfaces for the left and right optical paths, i.e.
the second surfaces 12R and 12L, the third surfaces 13R and 13L,
and the fourth surfaces 14R and 14L, as in the example shown in
FIG. 1. In this case, it is desirable that the at least three pairs
of reflecting surfaces should be formed from rotationally
asymmetric curved reflecting surfaces having the function of
correcting decentration aberrations.
[0036] The above-described optical path splitting element 10
according to the present invention can be used as at least a part
of a viewing optical system for distributing an image displayed by
a single image display device 1 to the left and right eyeballs of
an observer, as shown in FIG. 1, by way of example. In actuality,
it is desirable that the left and right ocular optical systems 20L
and 2OR should be placed in the left and right exiting optical
paths, whereby intermediate images 3L and 3R formed in the left and
right optical paths (in Example 1, intermediate images 3L and 3R
are formed within the prism between the fourth surfaces 14L and 14R
and the fifth surfaces 15L and 15R, respectively) are viewed as
enlarged images through the ocular optical systems 20L and 20R. In
this case, left and right exit pupils 4L and 4R of the left and
right viewing optical paths are formed at the respective exit sides
of the left and right ocular optical systems 20L and 20R.
Therefore, the observer's left and right eyes are placed at the
positions of the left and right exit pupils 4L and 4R to view the
enlarged intermediate images 3L and 3R.
[0037] Incidentally, the surface configurations of the surfaces of
the left and right optical systems, i.e. from the first surface 11
to the left and right fifth surfaces 15L and 15R, are determined so
that the configurations of the left and right axial principal rays
2L and 2R emanating from the image display device 1 and exiting
from the left and right fifth surfaces 15L and 15R as exit surfaces
are in 180-degree rotational symmetry with respect to a straight
line A-A' passing through the center of the display surface of the
image display device 1 at approximately right angles to the display
surface, as has been stated above. Accordingly, the left optical
system extending from the first surface 11 to the fifth surface 15L
and the right optical system extending from the first surface 11 to
the fifth surface 15R are in 180-degree rotational symmetry about
the straight line A-A'. Moreover, the left and right optical
systems are three-dimensionally decentered reflecting optical
systems. Therefore, the intermediate images 3L and 3R are generally
rotated through the same angle in the same direction about the
respective optical axes. Accordingly, an image naturally oriented
with respect to both the horizontal and vertical directions cannot
be observed unless the image display device 1, which is placed in
the object plane, is rotated in the opposite direction to the
direction of rotation of the intermediate images 3L and 3R through
the same angle as the angle of rotation about the straight line
A-A' as an axis of rotation so that the horizontal direction of the
image display area of the image display device 1 is at an angle to
a plane containing the left and right optical paths emerging from
the optical path splitting element 10 (in the case of a viewing
optical system for observation with two eyes, this plane is
parallel to a horizontal direction connecting the centers of the
pupils of the two eyes).
[0038] Incidentally, it is desirable to satisfy the following
condition:
10.degree.<.theta.<150.degree. (1)
[0039] where .theta. is the angle formed between the axial
principal rays 2L and 2R of left and right light beams led from
each pixel in the center of the image display device 1 to the left
and right eyes of the observer (i.e. the angle formed between the
axial principal rays 2L and 2R before being incident on the first
surface 11).
[0040] The condition (1) needs to be satisfied in order to separate
the image light beams for the two eyes appropriately. If .theta. is
not larger than the lower limit, i.e. 10.degree., the effective
diameter portions of the left and right optical surfaces,
particularly those of the first surfaces 2L and 2R undesirably
overlap each other. Accordingly, the optical system has to be
increased in size in order to ensure the required effective
diameter of each of the first surfaces 2L and 2R and hence becomes
unsuitable for use as the optical system of a head- or face-mounted
image display apparatus. Conversely, if .theta. is not smaller than
the upper limit, i.e. 150.degree., an image display device having
very wide viewing angle characteristics is needed to serve as the
image display device 1. At the same time, the solid angle of the
image light beam becomes small. As a result, it becomes impossible
to observe a bright image. Regarding the angle .theta., it is
preferable to satisfy the following condition:
15.degree.<.theta.<120.degree. (1-1)
[0041] In Example 1 (described later), .theta.=41.12.degree.. In
Example 2, .theta.=32.54.degree..
[0042] The above-described optical path splitting element 10 is
also usable to combine together rays in two optical paths by using
the optical paths reversely instead of splitting an optical path
from a single object as stated above.
[0043] The above-described image display apparatus can be used as
an image pickup apparatus in which an image pickup device is
provided in place of the image display device 1 in the
above-described arrangement. In this case, the exit pupils 4L and
4R are arranged as entrance pupils through which a light beam from
a subject passes, and a subject image is formed on the image pickup
device.
[0044] Further, the image display apparatus can be used as a
projection apparatus in which a projection object is provided in
place of the image display device 1 in the foregoing arrangement. A
screen is placed in front of the exit pupils 4L and 4R to form a
projected image of the projection object on the screen.
[0045] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0046] 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
[0047] FIG. 1 is a perspective view schematically showing the
surfaces and optical axes of a viewing optical system of an image
display apparatus according to Example 1 of the present
invention.
[0048] FIG. 2 is a perspective view schematically showing the
surfaces of the viewing optical system of the image display
apparatus according to Example 1 as seen from a direction different
from that in FIG. 1.
[0049] FIG. 3 is a perspective view schematically showing the
surfaces and right optical axis of a viewing optical system of an
image display apparatus according to Example 2 of the present
invention.
[0050] FIG. 4 is a perspective view showing the whole viewing
optical system of the image display apparatus according to Example
2 as seen from a direction different from that in FIG. 3.
[0051] FIG. 5 is a diagram for describing an anti-reflection member
and a distributed light reinforcing member usable in the present
invention.
[0052] FIG. 6 is a diagram showing the arrangement of an image
display apparatus according to the present invention as arranged to
be fitted for both eyes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] Examples 1 and 2 in which the optical path splitting element
according to the present invention is used in an image display
apparatus will be described below.
[0054] A coordinate system used in the following Examples is
defined as follows. The direction of the observer's visual axis
(forward direction) is defined as a Z-axis. The horizontal
direction of the observer is defined as an X-axis, and the vertical
direction of the observer is defined as a Y-axis.
[0055] In numerical data (shown later) in each Example, data is
shown with respect to the viewing optical system for the right eye
as data obtained by backward ray tracing from the exit pupil 4R for
the right eye to the image display device (image plane) 1.
Regarding the viewing optical system for the left eye, numerical
data is not shown. In Example 1, the viewing optical system for the
left eye has a configuration obtained by rotating the optical
system for the right eye through 180 degrees about the straight
line A-A' passing through the center (vertex position) of the image
display device (image plane) 1 at right angles thereto. In Example
2, a part of the left viewing optical system that extends from the
object plane to the intermediate image plane (IIM) of surface No. 5
is the same as that of the optical system for the right eye. The
remaining part of the viewing optical system for the left eye, i.e.
from the surface No. 6 to the image plane, has a configuration
obtained by rotating the corresponding part of the optical system
for the right eye through 180 degrees about a line (optical axis)
normal to the vertex position of the intermediate image plane
(IIM). The whole viewing optical system for the left eye is
constructed by horizontally moving the optical system so that the
image plane thereof is coincident with the image plane of the
optical system for the right eye.
[0056] In the following Examples 1 and 2, each optical path
splitting element 10 is formed from a three-dimensionally
decentered prism, which is decentered in three directions, i.e. X,
Y and Z directions. Examples 1 and 2 will be described below with
reference to the accompanying drawings.
EXAMPLE 1
[0057] FIG. 1 is a perspective view schematically showing the
surfaces and optical axes of a viewing optical system of an image
display apparatus according to Example 1.
[0058] FIG. 2 is a perspective view showing the surfaces of the
viewing optical system of the image display apparatus according to
Example 1 as seen from a direction different from that in FIG.
1.
[0059] The illustrated optical system is a viewing optical system
of the image display apparatus when arranged as a head-mounted
image display apparatus designed to be fitted for both eyes. The
viewing optical system includes an optical path splitting element
10 and a pair of ocular optical systems 20L and 20R (left and
right) . The optical path splitting element 10 is formed from a
decentered prism. The viewing optical system has a single image
display device 1 common to left and right optical systems. A
display light beam from the image display device 1 is split into
left and right beams through the optical path splitting element 10.
The beams are passed through the left and right ocular optical
systems 20L and 20R to project enlarged images of the image display
device 1 into the left and right eyeballs of an observer. The
optical path splitting element 10 has a first surface 11 as a
common entrance surface (refracting surface) through which left and
right axial principal rays 2L and 2R emanating from the image
display device 1 at an angle to each other enter the optical path
splitting element 10. Regarding the left optical path, the optical
path splitting element 10 has a second surface 12L, a third surface
13L, a fourth surface 14L, and a fifth surface 15L. The second
surface 12L reflects the left axial principal ray 2L entering
through the first surface 11. The third surface 13L reflects the
left axial principal ray 2L reflected from the second surface 12L.
The fourth surface 14L reflects the left axial principal ray 2L
reflected from the third surface 13L. The fifth surface 15L is an
exit surface (refracting surface) through which the left axial
principal ray 2L reflected from the fourth surface 14L exits the
optical path splitting element 10 so as to enter the left ocular
optical system 20L. Regarding the right optical path, the optical
path splitting element 10 has a second surface 12R, a third surface
13R, a fourth surface 14R, and a fifth surface 15R. The second
surface 12R reflects the right axial principal ray 2R entering
through the first surface 11. The third surface 13R reflects the
right axial principal ray 2R reflected from the second surface 12R.
The fourth surface 14R reflects the right axial principal ray 2R
reflected from the third surface 13R. The fifth surface 15R is an
exit surface (refracting surface) through which the right axial
principal ray 2R reflected from the fourth surface 14R exits the
optical path splitting element 10 so as to enter the right ocular
optical system 20R. The left and right reflecting surfaces 12L to
14L and 12R to 14R are formed from back-coated mirrors.
[0060] The surface configurations of the above-described surfaces,
i.e. from the first surface 11 to the left and right exit surfaces
15L and 15R, are determined so that the configurations of the left
and right axial principal rays 2L and 2R emanating from the image
display device 1 and exiting from the left and right fifth surfaces
15L and 15R as exit surfaces are in 180-degree rotational symmetry
with respect to a straight line A-A' passing through the center of
the display surface of the image display device 1 at approximately
right angles to the display surface. To form left and right optical
paths that are in 180-degree rotational symmetry with each other as
stated above, the optical path splitting element 10, which is a
decentered prism, is constructed by arranging the first surface 11,
the second surfaces 12R and 12L, the third surfaces 13R and 13L,
the fourth surfaces 14R and 14L, and the fifth surfaces 15R and 15L
so that when an optical system for the right optical path formed
from the first surface 11, the second surface 12R, the third
surface 13R, the fourth surface 14R and the fifth surface 15R is
rotated through 180 degrees about the straight line A-A', these
surfaces are coincident with the first surface 11, the second
surface 12L, the third surface 13L, the fourth surface 14L and the
fifth surface 15L, which form an optical system for the left
optical path.
[0061] The left and right axial principal rays 2L and 2R emerging
from the left and right exit surfaces (refracting surfaces) 15L and
15R of the optical path splitting element 10 extend parallel to
each other in the same direction. The left and right ocular optical
systems 20L and 20R are placed in the left and right optical paths.
The left and right ocular optical systems 20L and 20R are identical
with each other and each formed from two rotationally symmetric
lenses. In cooperation with the refracting surfaces of the left and
right exit surfaces 15L and 15R, the left and right ocular optical
systems 20L and 20R allow the intermediate images 3L and 3R formed
within the prism to be observed as enlarged images and also form
exit pupils 4L and 4R of the left and right optical systems at the
respective exit sides of the ocular optical systems 20L and
20R.
[0062] It should be noted that the ocular optical systems 20L and
20R may be formed from rotationally symmetric aspherical surfaces,
anamorphic surfaces, toric surfaces, or free-form surfaces to
cancel decentration aberrations produced in the optical path
splitting element 10. It is also possible to use spherical lenses
in a decentered position.
[0063] In this Example, a display device of 8.9.times.6.7
millimeters in size is used as the image display device 1. The
pupil diameter is 6 millimeters in the X-direction and 4
millimeters in the Y-direction. That is, each exit pupil is
rectangular. Regarding the viewing field angles, the horizontal
field angle is 25.degree., and the vertical field angle is
18.9.degree..
EXAMPLE 2
[0064] FIG. 3 is a perspective view schematically showing the
surfaces and right optical axis of a viewing optical system of an
image display apparatus according to Example 2. FIG. 4 is a
perspective view showing the whole viewing optical system as seen
from a direction different from that in FIG. 3.
[0065] The illustrated optical system is a viewing optical system
of the image display apparatus when arranged as a head-mounted
image display apparatus designed to be fitted for both eyes. The
viewing optical system uses an optical path splitting element 10
similar to that in Example 1. In Example 2, however, ocular optical
systems 20L' and 20R' are each formed by integrally cementing a
decentered prism to the exit surface side of the optical path
splitting element 10. The decentered prism is of the type in which
there are two internal reflections. Accordingly, the optical path
splitting element 10 has no fifth surfaces 15L and 15R.
[0066] Thus, the viewing optical system of Example 2 includes an
optical path splitting element 10 formed from a decentered prism
and left and right ocular optical systems 20L' and 20R' integrally
cemented to the optical path splitting element 10. The viewing
optical system has a single image display device 1 common to left
and right optical systems. A display light beam from the image
display device 1 is split into left and right beams through the
optical path splitting element 10. The beams are passed through the
left and right ocular optical systems 20L' and 20R' to project
enlarged images of the image display device 1 into the left and
right eyeballs of an observer. The part constituting the optical
path splitting element 10 has a first surface 11 as a common
entrance surface (refracting surface) through which left and right
axial principal rays 2L and 2R emanating from the image display
device 1 at an angle to each other enter the optical path splitting
element 10. Regarding the left optical path, the optical path
splitting element 10 has a second surface 12L, a third surface 13L,
and a fourth surface 14L. The second surface 12L reflects the left
axial principal ray 2L entering through the first surface 11. The
third surface 13L reflects the left axial principal ray 2L
reflected from the second surface 12L. The fourth surface 14L
reflects the left axial principal ray 2L reflected from the third
surface 13L. Regarding the right optical path, the optical path
splitting element 10 has a second surface 12R, a third surface 13R,
and a fourth surface 14R. The second surface 12R reflects the right
axial principal ray 2R entering through the first surface 11. The
third surface 13R reflects the right axial principal ray 2R
reflected from the second surface 12R. The fourth surface 14R
reflects the right axial principal ray 2R reflected from the third
surface 13R. The left and right reflecting surfaces 12L to 14L and
12R to 14R are formed from back-coated mirrors.
[0067] The surface configurations of the above-described surfaces,
i.e. from the first surface 11 to the left and right fourth
surfaces (reflecting surfaces) 14L and 14R, are determined so that
the configurations of the left and right axial principal rays 2L
and 2R emanating from the image display device 1 and reflected from
the left and right fourth surfaces 14L and 14R are in 180-degree
rotational symmetry with respect to a straight line A-A' (FIG. 1)
passing through the center of the display surface of the image
display device 1 at approximately right angles to the display
surface, as in the case of Example 1. To form left and right
optical paths that are in 180-degree rotational symmetry with each
other as stated above, the part constituting the optical path
splitting element 10, which is a decentered prism, is constructed
by arranging the first surface 11, the second surfaces 12R and 12L,
the third surfaces 13R and 13L, and the fourth surfaces 14R and 14L
so that when an optical system for the right optical path formed
from the first surface 11, the second surface 12R, the third
surface 13R and the fourth surface 14R is rotated through 180
degrees about the straight line A-A', these surfaces are coincident
with the first surface 11, the second surface 12L, the third
surface 13L and the fourth surface 14L, which form an optical
system for the left optical path.
[0068] The left and right axial principal rays 2L and 2R reflected
from the left and right reflecting surfaces 15L and 15R of the
optical path splitting element 10 are parallel to each other and
form intermediate images 3L and 3R before entering the parts
constituting the left and right ocular optical systems 20L' and
20R', which are decentered prisms. The ocular optical systems 20L'
and 20R' are identical with each other and in symmetry with respect
to a plane passing through the middle between the
parallel-reflected left and right axial principal rays 2L and 2R at
right angles to a plane containing the axial principal rays 2L and
2R. Therefore, only the arrangement for the right eye will be
described below. A light beam reflected from the fourth surface 14R
of the optical path splitting element 10 is incident on a first
surface 21R of the right ocular optical system 20R' at an angle
exceeding the critical angle. The first surface 21R also serves as
a third surface 23R, which is a refracting surface. Consequently,
the light beam is totally reflected by the first surface 21R and
then internally reflected by a second surface 22R. The reflected
light beam exits the right ocular optical system 20R' while being
refracted through the third surface 23R and passes through an exit
pupil 4R, thereby allowing the intermediate image 3R to be observed
as an enlarged image.
[0069] In this Example, a display device of 8.9.times.6.7
millimeters in size is used as the image display device 1. The
pupil diameter is 12 millimeters in the X-direction and 4
millimeters in the Y-direction. That is, each exit pupil is
rectangular. The difference in interpupillary distance among
observers is absorbed by increasing the exit pupil size of the
optical system in the X-direction. By doing so, it is possible to
omit a mechanical interpupillary distance adjusting mechanism.
Regarding the viewing field angles, the horizontal field angle is
30.degree., and the vertical field angle is 26.6.degree..
[0070] In this Example, a part of the left viewing optical system
that extends from the object plane to the intermediate image plane
(IIM) of surface No. 5 is the same as that of the optical system
for the right eye in the numerical data (shown later), as has been
stated above. The remaining part of the viewing optical system for
the left eye, i.e. from the surface No. 6 to the image plane, has a
configuration obtained by rotating the corresponding part of the
optical system for the right eye through 180 degrees about a line
(optical axis) normal to the vertex position of the intermediate
image plane (IIM) . The whole viewing optical system for the left
eye is constructed by horizontally moving the optical system so
that the image plane thereof is coincident with the image plane of
the optical system for the right eye. The optical path splitting
element for the right eye and the optical path splitting element
for the left eye are integrally formed as one unit. The optical
paths in the optical path splitting element 10 part are in
rotational symmetry with respect to a line perpendicular to the
center of the image display surface. The left and right optical
paths in the ocular optical system 20L' and 20R' are in plane
symmetry with each other.
[0071] Next, constituent parameters in the above-described Examples
1 and 2 will be shown. In the constituent parameters in each
Example, the right axial principal ray 2R is defined by a light ray
passing perpendicularly through the center of the right exit pupil
4R of the optical system and reaching the center of the image
display device 1 in the backward ray tracing. Further, in the
backward ray tracing, the center of the pupil 4R is defined as the
origin of each decentered optical surface constituting a decentered
optical system, as shown in FIGS. 1 and 3. The direction along
which the axial principal ray 2R travels from the pupil 4R toward
the ocular optical system 20R (20R') is defined as a Z-axis. The
direction in which the Z-axis extends from the pupil 4R toward the
ocular optical system 20R (20R') is defined as a positive direction
of the Z-axis. A horizontal plane is defined as an XZ-plane. A
vertical plane is defined as a YZ-plane. The direction in which the
X-axis extends leftward in the horizontal plane is defined as a
positive direction of the X-axis. The direction in which the Y-axis
extends upward in the vertical direction is defined as a positive
direction of the Y-axis.
[0072] Regarding decentered surfaces, each surface is given
displacements in the X-, Y- and Z-axis directions (X, Y and Z,
respectively) of the vertex position of the surface from the origin
of the optical system, and tilt angles (degrees) of the center axis
of the surface [the Z-axis of the above equation (a) in regard to
free-form surfaces; the Z-axis of the following equation (d) in the
case of aspherical surfaces] with respect to the X-, Y- and Z-axes
(.alpha., .beta. and .gamma., respectively). In this case, the
positive .alpha. and .beta. mean counterclockwise rotation relative
to the positive directions of the corresponding axes, and the
positive .gamma. means clockwise rotation relative to the positive
direction of the Z-axis. It should be noted that the way of
rotating the center axis of each surface through .alpha., .beta.
and .gamma. is as follows. First, the center axis of the surface
and the XYZ orthogonal coordinate system are rotated through
.alpha. counterclockwise about the X-axis. Then, the rotated center
axis of the surface is rotated through .beta. counterclockwise
about the Y-axis of the new coordinate system, and the coordinate
system once rotated is also rotated through .beta. counterclockwise
about the Y-axis. Then, the center axis of the surface, which has
been rotated twice, is rotated through .gamma. clockwise about the
Z-axis of the new coordinate system.
[0073] Among optical functional surfaces constituting the optical
system in each Example, a specific surface and a surface subsequent
thereto are given a surface separation when these surfaces form a
coaxial optical system. In addition, the refractive index and
Abbe's number of each medium are given according to the
conventional method.
[0074] The configuration of each free-form surface used in the
present invention is defined by the above equation (a) The Z-axis
of the defining equation is the axis of the free-form surface.
[0075] Aspherical surfaces used in the present invention are
rotationally symmetric aspherical surfaces given by the following
equation: 5 Z = ( y 2 / R ) / [ 1 + { 1 - ( 1 + K ) y 2 / R 2 } 1 /
2 ] + Ay 4 + By 6 + Cy 8 + Dy 10 + ( d )
[0076] In the above equation, Z is an optical axis (axial principal
ray) for which the direction of travel of light is defined as a
positive direction, and y is taken in a direction perpendicular to
the optical axis. R is a paraxial curvature radius, and K is a
conic constant. A, B, C, D . . . are 4th-, 6th-, 8th- and
10th-order aspherical coefficients, respectively. The Z-axis of
this defining equation is the axis of the rotationally symmetric
aspherical surface.
[0077] In the constituent parameters (shown later), those terms
concerning free-form surfaces and aspherical surfaces for which no
data is shown are zero. The refractive index is expressed by the
refractive index for the spectral d-line (wavelength: 587.56
nanometers). Lengths are given in millimeters.
[0078] It should be noted that in the tables showing constituent
parameters below, "IFFS" denotes a free-form surface, and "ASS"
denotes an aspherical surface. Further, "RE" denotes a reflecting
surface, and "IIM" denotes an intermediate image plane.
EXAMPLE 1
[0079]
1 Dis- Surface Radius of Surface placement Refractive Abbe's No.
curvature separation and tilt index No. Object .infin. -1000.00
plane 1 .infin. (Pupil) 2 38.54 (1) 1.5163 64.1 3 -27.34 (2) 4
12.90 (3) 1.5163 64.1 5 68.27 (4) 6 FFS{circle over (1)} (5) 1.5254
56.2 7 .infin. (IIM) (6) 1.5254 56.2 8 FFS{circle over (2)} (RE)
(7) 1.5254 56.2 9 FFS{circle over (3)} (RE) (8) 1.5254 56.2 10
FFS{circle over (4)} (RE) (9) 1.5254 56.2 11 ASS{circle over (1)}
(10) Image .infin. (11) plane ASS{circle over (1)} R -30.00 K
0.0000 FFS{circle over (1)} C.sub.4 -2.4491 .times. 10.sup.-2
C.sub.5 6.4179 .times. 10.sup.-3 C.sub.6 -7.5199 .times. 10.sup.-2
C.sub.7 -5.1391 .times. 10.sup.-4 FFS{circle over (2)} C.sub.4
-7.3339 .times. 10.sup.-3 C.sub.5 -1.8564 .times. 10.sup.-3 C.sub.6
-2.6281 .times. 10.sup.-3 C.sub.7 3.0118 .times. 10.sup.-5 C.sub.8
4.6653 .times. 10.sup.-5 C9 -5.8357 .times. 10.sup.-5 C.sub.10
-1.3736 .times. 10.sup.-4 FFS{circle over (3)} C.sub.4 -9.6533
.times. 10.sup.-3 C.sub.5 5.8402 .times. 10.sup.-4 C.sub.6 -9.1502
.times. 10.sup.-3 C.sub.7 -5.3656 .times. 10.sup.-5 C.sub.8 3.8709
.times. 10.sup.-5 C.sub.9 -2.6706 .times. 10.sup.-5 C.sub.10
-1.6587 .times. 10.sup.-5 FFS{circle over (4)} C.sub.4 1.9763
.times. 10.sup.-3 C.sub.5 4.8512 .times. 10.sup.-4 C.sub.6 -3.9217
.times. 10.sup.-3 C.sub.7 1.7853 .times. 10.sup.-4 C.sub.8 -1.0004
.times. 10.sup.-5 C.sub.9 2.5342 .times. 10.sup.-5 C.sub.10 7.4694
.times. 10.sup.-5 Displacement and tilt(1) X 0.00 Y 0.00 Z 30.00
.alpha. 0.00 .beta. 0.00 .gamma. 0.00 Displacement and tilt(2) X
0.00 Y 0.00 Z 35.00 .alpha. 0.00 .beta. 0.00 .gamma. 0.00
Displacement and tilt(3) X 0.00 Y 0.00 Z 36.00 .alpha. 0.00 .beta.
0.00 .gamma. 0.00 Displacement and tilt(4) X 0.00 Y 0.00 Z 41.00
.alpha. 0.00 .beta. 0.00 .gamma. 0.00 Displacement and tilt(5) X
0.00 Y 0.00 Z 49.00 .alpha. 0.00 .beta. 0.00 .gamma. 0.00
Displacement and tilt(6) X 0.00 Y 0.00 Z 54.35 .alpha. 0.00 .beta.
0.00 .gamma. 0.00 Displacement and tilt(7) X 0.00 Y 0.00 Z 57.00
.alpha. -6.86 .beta. 41.97 .gamma. 92.36 Displacement and tilt(8) X
44.00 Y 5.84 Z 53.00 .alpha. 10.81 .beta. -63.89 .gamma. -47.05
Displacement and tilt(9) X 32.00 Y 5.61 Z 35.00 .alpha. 174.77
.beta. 16.92 .gamma. -8.19 Displacement and tilt(10) X 32.00 Y 0.00
Z 63.00 .alpha. 0.00 .beta. 0.00 .gamma. 0.00 Displacement and
tilt(11) X 32.00 Y 0.00 Z 65.00 .alpha. 0.00 .beta. 0.00 .gamma.
8.61
EXAMPLE 2
[0080]
2 Dis- Surface Radius of Surface placement Refractive Abbe's No.
curvature separation and tilt index No. Object .infin. -1000.00
plane 1 .infin. (Pupil) 2 ASS{circle over (1)} (1) 1.5254 56.2 3
FFS{circle over (1)} (RE) (2) 1.5254 56.2 4 ASS{circle over (1)}
(RE) (1) 1.5254 56.2 5 .infin. (IIM) (3) 1.5254 56.2 6 FFS{circle
over (2)} (RE) (4) 1.5254 56.2 7 FFS{circle over (3)} (RE) (5)
1.5254 56.2 8 FFS{circle over (4)} (RE) (6) 1.5254 56.2 9
ASS{circle over (2)} (7) Image .infin. (8) plane ASS{circle over
(1)} R -83.20 K 0.0000 A 2.7572 .times. 10.sup.-6 B -8.0590 .times.
10.sup.-10 ASS{circle over (2)} R -16.07 K 0.0000 A 1.0135 .times.
10.sup.-4 FFS{circle over (1)} C.sub.4 -9.4211 .times. 10.sup.-3
C.sub.6 -1.0652 .times. 10.sup.-2 C.sub.8 4.9563 .times. 10.sup.-6
C.sub.10 4.2873 .times. 10.sup.-5 C.sub.11 -3.5143 .times.
10.sup.-8 C.sub.13 3.5874 .times. 10.sup.-7 C.sub.15 -7.1617
.times. 10.sup.-7 C.sub.17 -1.9762 .times. 10.sup.-8 C.sub.19
-3.5068 .times. 10.sup.-8 C.sub.21 -5.6908 .times. 10.sup.-8
FFS{circle over (2)} C.sub.4 -2.3265 .times. 10.sup.-4 C.sub.5
2.5719 .times. 10.sup.-3 C.sub.6 -5.6313 .times. 10.sup.-3 C.sub.7
-6.9711 .times. 10.sup.-5 C.sub.8 -4.6909 .times. 10.sup.-4 C.sub.9
6.8773 .times. 10.sup.-5 C.sub.10 -2.5412 .times. 10.sup.-4
C.sub.11 -7.9766 .times. 10.sup.-7 C.sub.12 -1.2161 .times.
10.sup.-5 C.sub.13 4.1658 .times. 10.sup.-6 C.sub.14 -8.8727
.times. 10.sup.-6 C.sub.15 2.2400 .times. 10.sup.-5 C.sub.16 1.6733
.times. 10.sup.-6 C.sub.17 5.6098 .times. 10.sup.-6 C.sub.18 6.2886
.times. 10.sup.-6 C.sub.19 6.5129 .times. 10.sup.-6 C.sub.20 2.6957
.times. 10.sup.-6 C.sub.21 1.2697 .times. 10.sup.-6 FFS{circle over
(3)} C.sub.4 -4.4861 .times. 10.sup.-3 C.sub.5 -1.3580 .times.
10.sup.-3 C.sub.6 -4.5982 .times. 10.sup.-3 C.sub.7 -5.0878 .times.
10.sup.-5 C.sub.8 2.6592 .times. 10.sup.-5 C.sub.9 -3.7474 .times.
10.sup.-5 C.sub.10 1.2026 .times. 10.sup.-5 C.sub.11 3.3957 .times.
10.sup.-7 C.sub.12 6.5363 .times. 10.sup.-8 C.sub.13 -5.0805
.times. 10.sup.-7 C.sub.14 2.7924 .times. 10.sup.-7 C.sub.15 1.9224
.times. 10.sup.-7 C.sub.16 4.7646 .times. 10.sup.-8 C.sub.17 5.7198
.times. 10.sup.-8 C.sub.18 8.5786 .times. 10.sup.-9 C.sub.19 6.0267
.times. 10.sup.-11 C.sub.20 3.6213 .times. 10.sup.-8 C.sub.21
2.4396 .times. 10.sup.-8 FFS{circle over (4)} C.sub.4 -6.9833
.times. 10.sup.-3 C.sub.5 -1.3736 .times. 10.sup.-4 C.sub.6 -7.4147
.times. 10.sup.-3 C.sub.7 2.5977 .times. 10.sup.-5 C.sub.8 -5.5362
.times. 10.sup.-7 C.sub.9 1.0948 .times. 10.sup.-5 C.sub.10 -1.2716
.times. 10.sup.-5 C.sub.11 4.4384 .times. 10.sup.-9 C.sub.12 8.2269
.times. 10.sup.-7 C.sub.13 9.9689 .times. 10.sup.-7 C.sub.14 1.7219
.times. 10.sup.-6 C.sub.15 6.6950 .times. 10.sup.-7 C.sub.16
-3.6728 .times. 10.sup.-8 C.sub.17 -6.3594 .times. 10.sup.-8
C.sub.18 1.5462 .times. 10.sup.-8 C.sub.19 1.1542 .times. 10.sup.-7
C.sub.20 -3.8596 .times. 10.sup.-8 C.sub.21 -8.4733 .times.
10.sup.-8 Displacement and tilt(1) X 0.00 Y 7.36 Z 29.28 .alpha.
20.75 .beta. 0.00 .gamma. 0.00 Displacement and tilt(2) X 0.00 Y
0.81 Z 40.18 .alpha. -12.75 .beta. 0.00 .gamma. 0.00 Displacement
and tilt(3) X 0.00 Y 27.08 Z 35.51 .alpha. 72.48 .beta. 0.00
.gamma. 0.00 Displacement and tilt(4) X 0.00 Y 35.49 Z 38.16
.alpha. 58.51 .beta. 41.34 .gamma. 62.89 Displacement and tilt(5) X
44.00 Y 36.44 Z 25.81 .alpha. 106.56 .beta. -60.73 .gamma. -83.58
Displacement and tilt(6) X 32.00 Y 19.81 Z 25.33 .alpha. -107.24
.beta. 18.41 .gamma. 8.59 Displacement and tilt(7) X 32.00 Y 47.11
Z 41.83 .alpha. 72.48 .beta. 0.00 .gamma. 0.00 Displacement and
tilt(8) X 32.00 Y 49.02 Z 42.44 .alpha. 72.48 .beta. 0.00 .gamma.
29.24
[0081] In the image display apparatus according to the present
invention, if a display light beam emitted from the image display
device 1 impinges on a boundary portion 5 (FIG. 2) between the left
and right reflecting surfaces 12L and 12R, which are positioned
closest to the entrance surface 11 of the optical path splitting
element 10 among the optical surfaces in the left and right optical
paths, the light beam may be reflected from the boundary portion 5
to become ghost light. Therefore, it is desirable that, as shown in
part (a) of FIG. 5, the boundary portion 5 and its vicinities
should be coated with a black paint or subjected to a diffusion
treatment to form an anti-reflection member 6 for preventing such
reflection, thereby absorbing or diffusing a light beam portion
(shown by the broken lines) of the display light beam 7 from the
image display device 1 that is incident on the boundary portion 5.
It should be noted that light beam portions of the display light
beam 7 that are shown by the solid lines are led to the left and
right optical paths as light beams effectively used for the
display.
[0082] When an image display device 8 having a small exit angle of
display light is used as the image display device 1, as shown in
part (b) of FIG. 5, it is desirable to place a light beam
distributing microprism 30 in correspondence to each pixel 9. The
light beam distributing microprism 30 has a sectional configuration
as shown in the figure by way of example to serve as a distributed
light reinforcing member whereby the exit angle of display light
emitted from each pixel 9 is increased in the directions of the
left and right optical paths. In place of the light beam
distributing microprism 30, a transmission type diffraction grating
arranged to weaken the intensity of zeroth-order transmitted light
and to intensify .+-.1 st-order diffracted light may be positioned
in close proximity to the display surface of the image display
device 1.
[0083] Incidentally, it is possible to form a stationary or
portable image display apparatus allowing observation with both
eyes by properly supporting the above-described viewing optical
system.
[0084] FIG. 6 shows the arrangement of the image display apparatus
designed to be fitted for both eyes. In FIG. 6, reference numeral
131 denotes a display apparatus body unit, which is fixed by a
support member through the observer's head so that the display
apparatus body unit 131 is held in front of both the observer's
eyes. The support member has a pair of front frames 132 (left and
right) each joined at one end thereof to the display apparatus body
unit 131. The left and right front frames 132 extend from the
observer's temples to the upper portions of his/her ears,
respectively. A pair of rear frames 133 (left and right) are joined
to the other ends of the front frames 132, respectively, and extend
over the side portions of the observer's head. The support member
further has a top frame 134 joined at both ends thereof to the
other ends of the left and right rear frames 133, respectively, so
that the top frame 134 supports the top of the observer's head.
[0085] A rear plate 135 is joined to one front frame 132 near the
joint to the rear frame 133. The rear plate 135 is formed from an
elastic member, e.g. a metal leaf spring. A rear cover 136, which
constitutes a part of the support member, is joined to the rear
plate 135 so that the rear cover 136 can support the apparatus at a
position behind the observer's ear in a region extending from the
back part of the head to the base of the neck. A speaker 139 is
mounted inside the rear plate 135 or the rear cover 136 at a
position corresponding to the observer's ear.
[0086] A cable 141 for transmitting external image and sound
signals is led out from the display apparatus body unit 131. The
cable 141 extends through the top frame 134, the rear frames 133,
the front frames 132 and the rear plate 135 and projects to the
outside from the rear end of the rear plate 135 or the rear cover
136. The cable 141 is connected to a video-replaying unit 140. It
should be noted that reference numeral 140a in the figure denotes a
switch and volume control part of the video-replaying unit 140.
[0087] The cable 141 may have a jack and plug arrangement attached
to the distal end thereof so that the cable 141 can be connected to
an existing video deck or the like. The cable 141 may also be
connected to a TV signal-receiving tuner so as to enable the user
to enjoy watching TV. Alternatively, the cable 141 may be connected
to a computer to receive computer graphic images or message images
or the like from the computer. To eliminate the bothersome cord,
the apparatus may be arranged to receive external radio signals
through an antenna connected thereto.
[0088] As will be clear from the foregoing description, the present
invention provides a compact optical path splitting element having
a reduced number of components and also provide an image display
apparatus using the optical path splitting element. That is, the
present invention provides an optical path splitting element having
at least two split axial principal rays each extending from the
center of an object to the center of an image. The optical path
splitting element uses a three-dimensional optical system in which
bent segments forming each of the axial principal rays lie in at
least two planes, thereby making the optical path splitting element
compact in size. At the same time, a power is given to the optical
path splitting element to reduce the number of components
thereof.
* * * * *