Optical: systems and elements – Prism – With reflecting surface
Reexamination Certificate
2002-01-08
2004-07-06
Shafer, Ricky D. (Department: 2872)
Optical: systems and elements
Prism
With reflecting surface
C359S631000, C359S633000, C359S637000
Reexamination Certificate
active
06760169
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prism optical element, an image observation apparatus and an image display apparatus. More particularly, the present invention relates to a head- or face-mounted image display apparatus that can be retained on the observer's head or face.
2. Discussion of Related Art
An example of a conventional head- or face-mounted image display apparatus, an image display apparatus disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 3-101709 (19910 is known. In this 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 convention image display apparatus. In this apparatus, 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.
U.S. Pat. No. 4,026,641 discloses another type of conventional image display apparatus. In the conventional image display apparatus, 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 reflecting surface.
U.S. Reissued Pat. No. 27,356 discloses another type of conventional image display apparatus. This apparatus is an ocular optical system designed to project an object surface onto an exit pupil by a semi-transparent concave mirror and a semitransparent plane mirror.
Other known image display apparatuses include those which are disclosed in U.S. Pat. Nos. 4,322,135 and 4,969,724, European Patent No. 0,583,116A2, and Japanese Patent Application Unexamined Publication (KOKAI) No. 7-333551 (1995).
However, an image display apparatus of the type in which an image of an image display device is relayed, as in Japanese Patent Application Unexamined Publication (KOKAI) No. 3-101709 (1991) and U.S. Pat. No. 4,669,810, 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.
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 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.
In an image display apparatus of the type in which an image of an image display device is projected into an observer's eyeball by using a toric reflecting surface as in U.S. Pat. No. 4,026,641, field curvature that is produced by the decentered toric reflecting surface is corrected by curving the object surface itself. Therefore, it is difficult to use a flat display, e.g. an LCD (Liquid Crystal Display), as an image display device.
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 in U.S. Reissued Pat. No. 27,356, 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 extremely compact image observation apparatus and image display apparatus which are capable of providing an observation image that is clear and has minimal aberration and minimal distortion even at a wide field angle, and a prism optical element for use in these apparatuses.
To attain the above-described object, the present invention provides a prism optical element formed from a plurality of surfaces facing each other across a medium having a refractive index (n) larger than 1 (n>1). The prism optical element has a first surface, a second surface, a third surface, and a fourth surface. The first surface has both a transmitting action through which light rays enter the prism optical element or exit therefrom and a reflecting action by which light rays are internally reflected in the prism optical element. The second surface is disposed to face the first surface across the medium and has a reflecting action by which light rays are internally reflected in the prism optical element. The third surface is disposed substantially close to the second surface to face the first surface across the medium and has a reflecting action by which light rays are internally reflected in the prism optical element. The fourth surface has such a transmitting action that when the first surface has an action through which light rays enter the prism optical element, the fourth surface has an action through which light rays exit from the prism optical element, whereas, when the first surface has an action through which light rays exit from the prism optical element, the fourth surface has an action through which light rays enter the prism optical element. The prism optical element satisfies the following condition:
sin
−1
(1/
n
d
)≦&thgr;
r3
≦60° (1)
where n
d
is the refractive index for the spectral d-line of the medium, and &thgr;
r3
is the angle of internal reflection of an arbitrary light ray at the third surface.
In the present invention, the arrangement of the second and third surfaces is not necessarily limited to the one in which surfaces designed separately from each other are disposed adjacent to each other, but includes an arrangement in which the second and third surfaces are formed by using one identical surface such that one region of the surface acts as the second surface, and another region of the surface acts as the third surface. In this case, an overlap region that acts as both the second and third surfaces may be present because a bundle of light rays has a width.
One image observation apparatus according to the present invention has an image forming device and an ocular optical system having an action by which an image formed by the image forming device is led to an eyeball of an observer. The ocular optical system
Takahashi Junko
Takahashi Koichi
Olympus Corporation
Pillsbury & Winthrop LLP
Shafer Ricky D.
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