Compact light path and package for liquid crystal projection displays

Abstract

An LCD projection display (,) houses a projection module (,) in which light propagates through an LCD module (,) at a shallow angle (,) that improves the contrast ration of and intentionally Keystones the image bearing light. The Keystoned light is reflected by a fold mirror (,) that is mounted at a 52° upward angle, which introduces more intentional Keystoning. A projection lens (,) is mounted coaxial to a tilted optical axis (,), but the Keystoned image bearing light is refracted about 10° off the optical axis and follows a Keystoning axis (,) through the projection lens. The light propagating from the projection lens is reflected by a main fold mirror (,) that is mounted at a 57° angle from the vertical to project the image bearing light onto a 10° slanted projection screen (,). Central light rays (,), image margin light rays (,), and the axial light rays (,) propagate unequal distances from the projection lens to the projection screen and are, therefore, unequally magnified to compensate for the Keystoning introduced by the LCD module. The steep mounting angle of the main fold mirror allows positioning it higher and more forward in the display, which reduces first surface reflections from ambient lighting and allows a significantly reduced depth dimension for the display.