Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reissue Patent
1999-05-21
2001-07-24
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S630000
Reissue Patent
active
RE037292
ABSTRACT:
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 P
1
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 {fraction (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 four
Takahashi Koichi
Togino Takayoshi
Mack Ricky
Olympus Optical Co,. Ltd.
Pillsbury Madison & Sutro LLP
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