PROJECTION TELEVISIONS WITH HOLOGRAPHIC SCREENS HAVING CENTER TO EDGE VARIATIONS

摘要

A projection screen (22) for a television has a three-dimensional hologram (26) on a film substrate (24). The screen (22) can have a plurality of stacked holograms and/or fresnel lenses having varying optical properties in vertical and horizontal directions. Image projectors (14, 16, 18) for different colors direct images which converge on a projection screen (22) formed by at least one hologram (26) on a light transmissive panel, collecting the converging light from the projectors (14, 16, 18) on the rear and displaying the images on a front with controlled light dispersion so as to orient the images substantially forward. The holographic screen (22) forms an interference array and has optical properties that vary horizontally and vertically across the field of view, in at least one of holographic gain, collimation and centering. Collimation is provided by at least one fresnel element, which can have a focal length that varies from a center point to the edges for improving edge brightness by directing light rays more inwardly toward a center axis. The center point can be displaced from the screen center, especially vertically, and the rate of change in fresnel focal length can be different proceeding in opposite directions or in different planes from the center point. Preferably the fresnel elements are linear lenticular fresnels.