Patent ID: 9482866
Filing Date: 2016-11-01
CPC Classification: G02B,G03B

Claim Text:
1. An optical projection system to enlarge an image on an image display element and project the enlarged image onto a screen, comprising: the image display element; a first optical system including lens groups arranged in order from an image display element side, a lens barrel holding the lens groups, and a free-form surface lens rotationally asymmetric and made from plastic; and a second optical system including a curved mirror disposed after the first optical system, wherein the free-form surface lens is formed to have a thickness which decreases from an intersection point between a surface of the free-form surface lens and an optical axis of the first optical system to an outer periphery of the lens along a line extending to the outer periphery, a shape of the free-form surface lens is symmetric relative to an X axis and asymmetric relative to a Y axis, the X axis being along a long side of the image display element and the Y axis being along a short side of the image display element, an apex of the surface of the free-form surface lens is located at an intersection point between the X and Y axes and on the optical axis of the first optical system, an optical effective area of the free-form surface lens is ±X1 along the X axis and from +Y1 to −Y2 along the Y axis, Y1 being smaller than Y2, and the thickness of the free-form surface lens is thickest at a reference point of the lens surface shape and thinnest at peripheral positions along the X and Y axes, the reference point being X=0, Y=0, the peripheral positions being X=±X1 and Y=−Y2.