Optics: image projectors – Relief illusion
Reexamination Certificate
2001-08-20
2003-09-02
Dowling, William (Department: 2851)
Optics: image projectors
Relief illusion
C353S078000, C359S479000, C359S629000
Reexamination Certificate
active
06612701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the field of optical display systems. More particularly, the invention pertains to apparatus and methods for enhancement of a real image projection system through the use of one or more aspheric mirrors or corrective aspheric optical curvatures.
2. Description of Related Art
The invention pertains to a real image projection system, and in particular, to a system in which an image of a real object is formed in space, giving the illusion that a real object exists at that point in space, when in reality it does not. A variation of this type of system has existed for many years in the form of various toys and magic tricks. Most are in the form of dual facing parabolic mirrors of equal focal lengths, known as 360 (i.e., 360°) displays, which create the illusion that a real object exists at the vertex of the upper curved mirror, but in which the real target object is actually located within the device itself, at the vertex of the lower curved mirror. Thus, the device creates the illusion of an object floating above the unit, when actually the object is positioned within the device at a different location.
U.S. Pat. No. 5,886,818, to Summer et al. (1999), the complete disclosure of which is hereby incorporated herein by reference, discloses a real image projection system having some features in common with the present invention.
U.S. Patent No. 3,647,284, to Elings (1972), the complete disclosure of which is hereby incorporated herein by reference, referred to hereinafter as the Elings patent, specifies parabolic, spherical, or ellipsoidal mirrors. The existing state of technology in 1972 would have made aspheric mirrors an impractical consideration. Thus, the device described in the Elings patent could have only functioned acceptably using two parabolic mirrors. Today's manufacturing technology, however, allows the production of aspheric optics in volume, and together with currently available desktop lens design software, makes the design and production of such complex optics possible. Parabolas are excellent for imaging at the focal point, but as one attempts to image larger objects where portions of the object are located substantially offset from the focal point, the effects of optical aberrations seriously degrade image quality. The aberrations and image degradation created by two spheres would have made the image nearly unrecognizable as the object being imaged. Ellipses have even more significant imaging problems. The parabola was the optimum solution in 1972, since production of aspheric optics of any size was not a practical option or something that one skilled in the art would even consider designing or building. Recent technological advances in lens manufacturing now make aspheric reflectors a practical solution to a difficult imaging problem.
An asphere is an optimized curve, significantly deviating from the other conic family of curves, such as spheres, parabolas, hyperbolas, and ellipses. Aspheres have very non-uniform curve changes that are specifically designed to counteract and minimize the aberrations that are natural phenomena of other curve families, especially for imaging off-axis or offset from the focal point.
U.S. Pat. No. 4,802,750, to Welck (1989), the complete disclosure of which is hereby incorporated herein by reference, referred to hereinafter as the Welck patent, discloses two facing parabolic segments of equal focal length, each being positioned such that its vertex is coincident with the focal point of the other. The light-path is transmitted from the focal point of the first parabolic mirror segment and is reflected off of the first parabolic reflector surface as collimated light (i.e., the reflected rays emanating from any one point source are substantially parallel to all other reflected rays emanating from the same source point, regardless of where on the curved surface it reflects from) as it is reflected to the second facing parabolic mirror, forming an image at the focal point of the second parabolic mirror. Maintaining a collimated or parallel light path between the two reflector surfaces is important to minimize the effects of aberrations, which is a natural phenomenon of curved optics, such as parabolic mirrors. The present invention differs substantially, in that the system of the Welck patent is limited to equal focal length parabolic segments, and is defined as an off-axis system. The Welck patent differs from the Elings patent, in that it uses “compound curvilinear surfaces of revolution”. Although the mirrors disclosed in the Welck patent are defined as having a “compound curvilinear” surface of revolution, the Welck patent is clearly limited to parabolic surfaces.
In a conventional configuration, such as the Welck patent, using two parabolic mirrors of equal focal lengths, the light-path between the two parabolic reflectors is collimated when the image is projected at a “one-to-one” unmagnified condition. To create a de-magnified image using this configuration, the actual target object must be moved to a position other than the focal point. The result of de-magnifying with this method is that the light-path between the two parabolic mirrors is no longer collimated or parallel, and the effects of aberrations become more apparent, thus causing degradation of the projected image. As the image moves away from the focal point, the image quality degrades substantially. This is a natural and inherent problem with parabolic systems used off-axis, or when imaging at a point other than the focal point of the optical elements. An aspheric curve can be optimized to counteract and minimize such aberrations.
There are significant advantages to projecting a de-magnified image with improved imagery. A de-magnified image has a higher resolution per square inch. As an example, a standard 5″ LCD panel measuring 3″ high by 4″ wide, with 640 by 480 resolution has a resolution of 160 pixels per inch in both the horizontal and vertical direction, or 25,600 pixels per square inch. A real image projected by the present invention, using two unequal focal length mirror segments (e.g., one at 80% of the other, or an 80% de-magnification), at least one of which is aspheric in shape, results in a real image pixel density of 200 pixels per inch in both horizontal and vertical direction, thus resulting in an image pixel density of 40,000 pixels per square inch. Thus, the resulting resolution of the image is 156% of the resolution of the actual target LCD screen. The density of a real image relates directly to how solid and, thus, how real the image appears to the eye. This is of significance in preventing image “bleed-through” of the background scene or image.
A second benefit of the present invention is that it increases the brightness per square inch of the projected real image, as compared to the actual target object, with significantly less image degradation. As an example, the system using a LCD panel that produces 200 lumens per square inch produces an image that provides 230 lumens per square inch (assuming that the two reflectors each have a reflectivity of 96% and the system has two different focal lengths, one being 80% of the other). In contrast, prior art systems, such as those described in the Elings and Welck patents, produce a real image having a brightness of only 184 lumens per square inch (assuming that the mirrors also have 96% reflective coatings and the systems are used in a 1× magnification or equal focal lengths reflectors, as they are described).
An additional benefit of the present invention is that the optical orientation of the two aspheric mirrors optionally can be reversed, so that the axis of the longer focal length segment is parallel to the viewing axis, thus producing a magnified image at an increased projection distance. The two different focal length mirrors optionally are combined in four different orientations. For example, in a system using a 10″ focal length mirror and a 12″ focal length mirror, four separate
Robinson Douglas L.
Turner Randolph J.
Westort Kenneth S.
Brown & Michaels PC
Dowling William
Optical Products Development Corporation
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