Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reissue Patent
1999-08-26
2002-03-12
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
C359S631000, C359S637000
Reissue Patent
active
RE037579
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. 20
shows the optical system of the conventional image display apparatus. As illustrated in the figure, in the conventional image display apparatus, an image that is displayed by an image display device is transmitted as an aerial image by a relay optical system including a positive lens, and the aerial image is projected into an observer's eyeball as an enlarged image by an ocular optical system formed from a concave reflecting mirror.
Japanese Patent Application Unexamined Publication (KOKAI) No. 62-214782 (1987) discloses another type of conventional image display apparatus. As shown in FIGS.
21
(
a
) and
21
(
b
), the conventional image display apparatus is designed to enable an image of an image display device to be directly observed as an enlarged image through an ocular lens.
U.S. Pat. No. 4,026,641 discloses another type of conventional image display apparatus. In the conventional image display apparatus, as shown in
FIG. 22
, an image of an image display device is transferred to a curved object surface by an image transfer device, and the image transferred to the object surface is projected in the air by a toric reflector.
U.S. Reissued Pat. No. 27,356 discloses another type of conventional image display apparatus. As shown in
FIG. 23
, the apparatus is an ocular optical system designed to project an object surface on an exit pupil by a semitransparent concave mirror and a semitransparent plane mirror.
However, an image display apparatus of the type in which an image of an image display device is relayed, as in the image display apparatus shown in
FIG. 20
, must use several lenses as a relay optical system in addition to an ocular optical system, regardless of the type of ocular optical system .Consequently, the optical path length increases, and the optical system increases in both size and weight.
In a layout such as that shown in FIGS.
21
(
a
) and
21
(
b
), the amount to which the apparatus projects from the observer's face undesirably increases. Further, since an image display device and an illumination optical system are attached to the projecting portion of the apparatus, the apparatus becomes increasingly large in size and heavy in weight.
Since a head-mounted image display apparatus is fitted to the human body, particularly the head, if the amount to which the apparatus projects from the user's face is large, the distance from the supporting point on the head to the center of gravity of the apparatus is long. Consequently, the weight of the apparatus is imbalanced when the apparatus is fitted to the observer's head. Further, when the observer moves or turns with the apparatus fitted to his/her head, the apparatus may collide with something.
That is, it is important for a head-mounted image display apparatus to be small in size and light in weight An essential factor in determining the size and weight of the apparatus is the layout of the optical system.
However, if an ordinary magnifier alone is used as an ocular optical system, exceedingly large aberrations are produced, and there is no device for correcting them. Even if spherical aberration can be corrected to a certain extent by forming the configuration of the concave surface of the magnifier into an aspherical surface, other aberrations such as coma and field curvature remain. Therefore, if the field angle for observation is increased, the image display apparatus becomes impractical. Alternatively, if a concave mirror alone is used as an ocular optical system it is necessary to use not only ordinary optical elements (lens and mirror) but also a device for correcting field curvature by an image transfer device (fiber plate) having a surface which is curved in conformity to the field curvature produced, as shown in FIG.
22
.
In a coaxial ocular optical system in which an object surface is projected on an observer's pupil by using a semitransparent concave mirror and a semitransparent plane mirror, as shown in
FIG. 23
, since two semitransparent surfaces are used, the brightness of the image is reduced to as low a level as {fraction (1/16)}, even in the case of a theoretical value. Further, since field curvature that is produced by the semi-transparent concave mirror is corrected by curving the object surface itself, it is difficult to use a flat display, e.g. an LCD (Liquid Crystal Display), as an image display device.
SUMMARY OF THE INVENTION
In view of the above-described problems of the conventional techniques, an object of the present invention is to provide an image display apparatus which enables observation of a clear image at a wide field angle with substantially no reduction in the brightness of the observation image, and which is extremely small in size and light in weight and hence unlikely to cause the observer to be fatigued.
To attain the above-described object, the present invention provides a first image display apparatus which includes an image display device for displaying an image, and an ocular optical system for projecting the image formed by the image display device and for leading the projected image to an observer's eyeball. The ocular optical system is arranged such that light rays emitted from the image display device are reflected three or higher odd-numbered times before reaching the observer's eyeball, and that a surface of the ocular optical system that is disposed immediately in front of the observer's eyeball is a refracting surface which internally reflects the light rays, and through which the light rays exit from the ocular optical system.
In addition, the present invention provides a second image display apparatus which includes an image display device for displaying an image, and an ocular optical system for projecting the image formed by the image display device and for leading the projected image to an observer's eyeball. The ocular optical system is arranged such that light rays emitted from the image display device are reflected three times before reaching the observer's eyeball, and that a surface of the ocular optical system that is disposed immediately in front of the observer's eyeball is a refracting surface which internally reflects the light rays, and through which the light rays exit from the ocular optical system.
In addition, the present invention provides a third image display apparatus which includes an image display device for displaying an image, and an ocular optical system for projecting the image formed by the image display device and for leading the projected image to an observer's eyeball.
The ocular optical system has at least three surfaces, and a space formed by the at least three surfaces is filled with a medium having a refractive index larger than 1. The at least three surfaces include, in the order in which light rays pass in backward ray tracing from the observer's eyeball to the image display device, a first surface which functions as both a refracting surface and an internally reflecting surface, a second surface which is a reflecting surface facing the first surface and decentered or tilted with respect to an observer's visual axis, and a third surface which is a refracting surface closest to the image display device, so that reflection takes place three times in the path from the observer's eyeball to the image display device.
In addition, the present invention provides a fourth image display apparatus which includes an image display device for displaying an image, and an ocular optical system for projecting the image formed by the image display device and for leading the projected image to an observer's eyeball. The ocul
Mack Ricky
Olympus Optical Co,. Ltd.
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