Patent ID: 7467872

Claim:
A projection optical unit for use in a projection type image display device, comprising: a first optical system including at least one free-shaped-surface lens having a rotationally asymmetrical free shaped surface for enlarging light from an image display element; and a second optical system including at least one free-shaped-surface mirror having a rotationally asymmetrical free shaped reflection surface for reflecting the light from the first optical system, wherein a picture plane center ray emitted from a center of a display picture plane of the image display element passes through the first optical system, the second optical system, and a flat reflection mirror to enter the screen obliquely with respect to a normal of the screen in a ease where the light reflected by the free-shaped-surface mirror of the second optical system is reflected by the flat reflection mirror and projected onto the screen, wherein: the first optical system includes a front group including lenses having rotationally symmetrical shapes, and a rear group including the at least one free-shaped-surface lens; and assuming that a distance of a path of a ray entering an upper end of the screen from the reflection surface of the second optical system is L 1 , a distance of a path of a ray entering a lower end of the screen from the reflection surface of the second optical system is L 2 , a distance between the upper end and the lower end of the picture plane of the screen is Dv, and an angle formed by the picture plane center ray and the normal of the screen is θs in a plane including the picture plane center ray and the normal of the screen in a position where the picture plane center ray enters, the following expression is satisfied: | L 1 −L 2|<1.2*sin θ s*Dv.