Image display apparatus

#The present invention relates to an image display apparatus which is retained on the observer's head. More particularly, the present invention relates to a headmounted display apparatus having a magnification varying function.

#In a conventional head-mounted display apparatus, an image formed by an image display device is projected on an observer's eyeball at an initially set angle of view, as described in Japanese Patent Application Laid-Open (KOKAI) No. 03-188777 (1991). However, when the angle of view is fixed as in the conventional apparatus, various problems may arise according to the kind of image for observation. That is, when the angle of view is set relatively wide, as shown in FIG. 11(a), the magnification becomes high. However, an image seen at such a wide angle of view makes the observer feel a sensation of pressure and causes him or her to feel easily fatigued when observing such an image for a long time. In addition, since the pixels of the image display device are enlarged at a high magnification, curved lines of the displayed image are seen as uneven lines of pixels, as illustrated in FIG. 11(a). When the angle of view is set relatively narrow, as shown in FIG. 11(b), the image frame becomes small, so that the displayed image lacks force, and an image composed of fine lines becomes invisible.

#In the conventional head-mounted display apparatus having a fixed angle of view, if an image according to NTSC, which has an aspect ratio of 4:3, is changed over to an image according to HDTV, which has an aspect ratio of 16:9, as described, for example, in Japanese Patent Application Laid-Open (KOKAI) No. 04-177986 (1992), the top and bottom of the image frame are cut, which makes the observer feel the images reduced in force.

#FIGS. 1(a)-1(c) show one example of the optical system of a head-mounted display apparatus according to a first embodiment of the present invention.

#FIG. 2 schematically shows the optical system of a modification of the first embodiment.

#FIGS. 3(a) and 3(b) illustrate one example of application of a variable magnification optical system according to the present invention.

#The present invention is basically arranged such that the projection optical system of an image display apparatus, e.g., a head-mounted display apparatus, is provided with a magnification varying function, thereby enabling the user to select a desired angle of view for observation. In addition, when the aspect ratio is to be changed so that the image frame becomes wide relative to the frame height, for example, the magnification is automatically raised. To obtain the magnification varying function with a compact arrangement, a relay optical system is used, and a part or the whole of the optical system is rotated about an axis perpendicular to the optical axis to thereby vary the magnification. By using electronic zooming in combination with the above-described arrangement, continuous zooming can be realized. In addition, it is possible to observe a distortion-free image at all times by detecting a state of the variable magnification optical system, and correcting an image to be displayed on the image display device so that the image distortion caused by the optical system is canceled.

#Embodiments of the present invention will be described below with reference to the accompanying drawings.

#FIGS. 1(a)-1(c) show one example of the optical system of a turret variable magnification head-mounted display apparatus according to a first embodiment of the present invention. In the FIGS., 1(a), 1(b) and 1(c) show the optical system when set at a low magnification, a medium magnification and a high magnification are depicted, respectively, by a magnification changeover operation. Rays of light emerging from an image display device 11, e.g., a liquid crystal display device, are led through a first relay optical system 12 to a second relay optical system 13. The second relay optical system 13 is arranged so that the object and image surfaces thereof lie in the same plane, as described later. The second relay optical system 13 is disposed so that the image surface of the first relay optical system 12 is coincident with the object surface (image surface) of the second relay optical system 13. An image formed by the second relay optical system 13 is projected on an eyeball 15 of a user of the head-mounted display apparatus by an ocular optical system 14.