Abstract: The invention relates to a slimmed-down yet high-performance image display device which comprises a decentered prism capable of internal reflection and a reflection type image display device such as a reflection-type LCD or DMD and can present bright images to an observer, and provides an image display apparatus comprising a light source 5, a reflection type image display device 3, and an ocular optical system for guiding an image displayed on device 3 into an eyeball position for forming an intermediate image 4. The ocular optical system comprises a prism member 10 comprising an entrance surface 11 and two reflecting surfaces 12 and 13. In a prism, an optical path for connecting the first surface 11 with the second surface 12 intersects a reflecting optical path from the third surface 13. The ocular optical system further comprises a back-coated reflecting surface 23 between the third surface 13 and an observer's eyeball side.

Abstract: A viewing optical system and an image-forming optical system, in which an intermediate image is formed once and two decentered prisms, i.e. first and second prisms, are arranged to correct each other's decentration aberrations, thereby attaining a wide viewing field angle and a short focal length. The second prism is placed closer to the image side than the first prism and has four optical surfaces, of which a first surface is an entrance surface, second and third surfaces are reflecting surfaces, and a fourth surface is an exit surface. In the second prism, an optical path crosses itself. At least one of the second and third surfaces has a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration. The first prism has a reflecting surface, an entrance surface, and an exit surface. The reflecting surface has a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration.

Abstract: A transmitted illumination type meter comprises a transparent light transmitting board having both a light entering bore and a shaft passing bore formed therethrough; a translucent dial plate placed on a front surface of the board, the dial plate having a shaft passing opening mated with the shaft passing bore of the board; a movement positioned behind the board; a light source positioned within the light entering bore; a drive shaft extending from the movement to the outside of the dial plate through the shaft passing bore and the shaft passing opening; a transparent pointer connected to the drive shaft to move over a front surface of the dial plate; and an annular convex peripheral wall defining the light entering bore. The annular convex peripheral wall allows light beams from the light source to enter the board and travel in parallel in the same. A plurality of stepped annular light reflecting surfaces are formed on a rear surface of the board and arranged to be concentric with the light entering bore.