A projection-type television receiver comprising right, left and center projection tubes each having a face, the images on the faces of the right and left tubes being formed in registry with the center of each corresponding face for minimizing keystone distortion and maximizing luminance in the receiver,...http://www.google.com/patents/US4730211?utm_source=gb-gplus-sharePatent US4730211 - Projection-type color television receiver wherein the center lines of right and left projection lenses intersect a display screen at points which are offset from a point at which the center line of a center projection lens intersects the display screen
