Abstract: A video image rotating apparatus includes a rear projection screen rotatably disposed in a generally horizontal plane, thus allowing only a single mirror to be angularly positioned over the screen to project video images to viewers. An optical system is positioned below the screen and vertically aligned therewith for projecting video images onto the screen. Preferably, the video images are mechanically rotated by rotating a portion of the optical system at a rate of rotation that is one-half that of the screen so that all viewers surrounding the video image rotating apparatus will see the same picture substantially simultaneously and continuously. Alternatively, the video images produced by the optical system may be rotated by an electronic image rotation system that electronically rotates the images produced in synchronization with rotation of the screen.

Abstract: A video image rotating apparatus includes a rear projection screen rotatably disposed in a generally horizontal plane, thus allowing only a single mirror to be angularly positioned over the screen to project video images to viewers. An optical system is positioned below the screen and vertically aligned therewith for projecting video images onto the screen. Preferably, the video images are mechanically rotated by rotating a portion of the optical system at a rate of rotation that is one-half that of the screen so that all viewers surrounding the video image rotating apparatus will see the same picture substantially simultaneously and continuously. Alternatively, the video images produced by the optical system may be rotated by an electronic image rotation system that electronically rotates the images produced in synchronization with rotation of the screen.

Abstract: An INVAR 36 material having long-term dimensional stability is produced by sintering a blend of powders of nickel and iron under pressure in an inert atmosphere to form an alloy containing less than 0.01 parts of carbon and less than 0.1 part aggregate and preferably 0.01 part individually of Mn, Si, P, S, and Al impurities. The sintered alloy is heat treated and slowly and uniformly cooled to form a material having a coefficient of thermal expansion of less than 1 ppm/.degree.C. and a temporal stability of less than 1 ppm/year.