Abstract: A method for producing a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, and the object light either having diffusing and scattering characteristics or being passed through an optical diffusion body, mainly includes the following steps: In a first step, a ratio &eegr;R0/&eegr;00 of a first diffraction efficiency &eegr;00 and a second diffraction efficiency &eegr;R0, is calculated. The diffraction efficiency &eegr;00 is dependent on two object light beams. The efficiency &eegr;R0 is dependent on the object light and the reference light. In a second step, the intensity E0 of the object light and the intensity ER of the reference light is adjusted in such a way that the ratio &eegr;R0/&eegr;00 is set to at least 10 and the efficiency &eegr;00 does not exceed 5%.

Abstract: A method for producing a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, and the object light either having diffusing and scattering characteristics or being passed through an optical diffusion body, mainly includes the following steps: In a first step, a ratio &eegr;RO/&eegr;OO of a first diffraction efficiency &eegr;OO and a second diffraction efficiency &eegr;RO, is calculated. The diffraction efficiency &eegr;OO is dependent on two object light beams. The efficiency &eegr;RO is dependent on the object light and the reference light. In a second step, the intensity EO of the object light and the intensity ER of the reference light is adjusted in such a way that the ratio &eegr;RO/&eegr;OO is set to at least 10 and the efficiency &eegr;OO does not exceed 5%.

Abstract: A method for producing a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, and the object light either having diffusing and scattering characteristics or being passed through an optical diffusion body, mainly includes the following steps: In a first step, a ratio .eta..sub.R0 /.eta..sub.00 of a first diffraction efficiency .eta..sub.00 and a second diffraction efficiency .eta..sub.R0, is calculated. The diffraction efficiency .eta..sub.00 is dependent on two object light beams. The efficiency .eta..sub.R0 is dependent on the object light and the reference light. In a second step, the intensity E.sub.O of the object light and the intensity E.sub.R of the reference light is adjusted in such a way that the ratio .eta..sub.R0 /.eta..sub.00 is set to at least 10 and the efficiency .eta..sub.00 does not exceed 5%.

Abstract: A display producing a display image in a vehicle width mark form and an optical path changing device directing the display image to a windshield are mounted on a base. The base is driven by an arc drive portion along an arcuate path with an arc center which is an intersection of a first imaginary sight line and a second imaginary sight line. The imaginary sight lines are reflections of a first and second actual sight lines in which a driver looks at the image position. Since the arc center conjugates the image position, when the display and the optical path changing device move along the arcuate path, the display image projecting on the windshield changes, and therefore, the image does not move up and down from the ground. Further, when a distance between the display and the optical path changing device changes, since the base moves along the arcuate path, the display distance of the image changes and the image moves along the surface of the ground.

Abstract: A rear indicator device for an automobile arranged inwardly of and adjacent to a rear window. The device includes a light guide plate 2, a hologram 2 arranged in the light guide plate 2 and an irregular shaped prism having a first section having an apex angle .phi.1 at which the light beam from a light source 5 is subjected to a refraction so that the light beam is flattened. The flattened beam is again introduced into the prism at a second section which is in face to face contact with the light guide plate 2, so that the light beam is transmitted inside the light guide plate 2 toward the hologram 3, whereat the light beam is introduced into the hologram at a predetermined angle of incidence, so that a horizontal light beam of a predetermined wave length is obtained in a rear direction of the automobile to indicate the braking of the automobile.