Image display apparatus comprising an internally reflecting ocular optical system

Abstract

An image display apparatus which enables observation of a clear image at a wide field angle with substantially no reduction in the brightness of the observation image, and which is extremely small in size and fight in weight and hence unlikely to cause the observer to be fatigued. The image display apparatus includes an image display device and an ocular optical system for projecting an image formed by the image display device and for leading the projected image to an observer's eyeball. The ocular optical system (3) has three surfaces, and a space formed by the three surfaces is filled with a medium having a refractive index larger than 1. The three surfaces include, in the order in which light rays pass in backward ray tracing from the observer's eyeball (1) to the image display device (4), a first surface (5) which functions as both a refracting surface and an internally reflecting surface, a second surface (6) which is a reflecting surface facing the first surface (5) and decentered or tilted with respect to an observer's visual axis (2), and a third surface (7) which is a refracting surface closest to the image display device (4), so that reflection takes place three times in the path from the observer's eyeball (1) to the image display device (4).

Description

BACKGROUND OF THE INVENTIONThe 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 ...

AI Technical Summary

Benefits of technology

In this apparatus, light rays emitted from the image display device are reflected three times in the ocular optical system, thereby enabling the light rays to be folded very effectively and favorably, and thus succeeding in minimizing the thickness of the ocular optical system and realizing reduction in both size and weight of the image display apparatus. Light rays emanating from the observer's pupil is first reflected toward the observer's face. Then, by the second reflection, the light rays are reflected forwardly from the observer's face side. By the third reflection, the light rays are reflected toward the observer's face again to reach the image display device. Therefore, the image display device lies closer to the observer, and the image display device can be disposed in such a manner that a side thereof which is reverse to its display surface faces the observer. Accordingly, it is possible to realize a head-mounted image display apparatus which projects from the observer's face to an extremely small amount for the same reasons as set forth above with respect to the second image display apparatus according to the present invention. Although it is possible to obtain similar advantageous effects by arranging the ocular optical system such that the fight rays are reflected five or higher odd-numbered times, an increase in the number of reflections causes the distance from the image display device to the observer's pupil position to lengthen exceedingly. Consequently, it becomes necessary to use longer and larger optical elements. Further, it becomes difficult to ensure a wide field angle because the focal length of the ocular optical system becomes long. Accordingly, the use of the ocular optical system which allows the image of the image display device to reach the observer's eyeball by three reflections makes it possible to realize a well-balanced image display apparatus.

by arranging the ocular optical system such that the fight rays are reflected five or higher odd-numbered times, an increase in the number of reflections causes the distance from the image display device to the observer's pupil position to lengthen exceedingly. Consequently, it becomes necessary to use longer and larger optical elements. Further, it becomes difficult to ensure a wide field angle because the focal length of the ocular optical system becomes long. Accordingly, the use of the ocular optical system which allows the image of the image display device to reach the observer's eyeball by three reflections makes it possible to realize a well-balanced image display apparatus.

Further, a surface of the ocular optical system that is disposed immediately in front of the observer's face is adapted to perform both refraction and reflection. Therefore, it is possible to reduce the number of surfaces needed to form the ocular optical system and hence possible to improve productivity. In addition, if the angle of internal reflection at the first surface is set so as to be larger than the critical angle, it becomes unnecessary to provide the first surface with a reflective coating. Therefore, even if the transmitting and reflecting regions on the first surface overlap each other, the image of the image display device reaches the observer's eyeball without any problem. Accordingly, the ocular optical system can be arranged in a compact form, and the field angle for observation can be widened.

In the third image display apparatus according to the present invention, 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. Examples 1 to 5 (described later) correspond to the arrangement of the third image display apparatus.

In this apparatus, a space that is formed by the first, second and third surfaces of the ocular optical system is filled with a medium having a refractive index larger than 1, and light rays emitted from the image display device are reflected three times in the ocular optical system, thereby enabling the light rays to be folded very effectively and favorably, and thus succeeding in minimizing the thickness of the ocular optical system realizing reduction in both size and weight of the image display apparatus, and providing the observer with a clear observation image having a wide exit pupil diameter and a wide field angle.

By filling the space formed by the first, second and third surfaces with a medium having a refractive index larger than 1, light rays from the pupil are refracted by the first surface, and it is therefore possible to minimize the height at which extra-axial principal and subordinate rays are incident on the second surface. Consequently, the height of the principal ray at the second surface is low, and therefore, the size of the second surface is minimized. Thus, the ocular optical system can be formed in a compact structure. Alternatively, the field angle can be widened. Further, because the height of the subordinate rays is reduced, it is possible to minimize comatic aberrations produced by the second surface, particularly higher-order comatic aberrations.

Problems solved by technology

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.

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.

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.

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.

Therefore, if the field angle for observation is increased, the image display apparatus becomes impractical.

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.

Images