1. Field of the Invention
The present invention relates to a head-mounted image display apparatus.
2. Description of the Prior Art
Conventional methods of obtaining high realism in an image display apparatus that directs image light based on a displayed image to the user's pupil include a method in which a displayed image is projected onto the user's pupil as a virtual image without an intermediate image being formed and a method in which a displayed image is projected onto a screen and the user views the image. These methods are advantageous in that a wide viewing angle and a large pupil diameter are comparatively easily obtained and high realism is obtained.
However, in the method in which a virtual image is projected onto the user's eye without an intermediate image being formed, a multiplicity of large-diameter lens elements are necessary to achieve a wide viewing angle and a large pupil diameter, which increases the cost of the optical system and the weight. On the other hand, the method in which an image is projected onto a screen and the user views the image is advantageous in that a large pupil diameter can be achieved by diffusion by the screen and that the projection optical system can be made compact. FIG. 7 schematically shows the structure of the optical system of a conventional head-mounted image display apparatus based on this method.
An image display element 53 is illuminated by a lighting source 52, and the image light based on the image display exits from a projection optical system 54. The image light is reflected at a half mirror 51 and projected onto a reflective screen 56 to form an image. The reflected light from the screen 56 is transmitted by the half mirror 51 and supplied to the user's pupil EP. By this light, the user views the image on the screen 56.
However, in the conventional image display apparatus using a screen, the screen is fixed in front of the user. That is, since the screen is disposed away from the head, the overall mass moment of the apparatus imposed on the user's head is great, so that the load on the user when he or she wears the apparatus on his or her head is heavy.