Patent ID: 7780296

Claim:
A projection optical unit for obliquely projecting an image displayed on an image display element upon a projection surface, enlargedly, comprising: a lens group, being disposed neighboring to said image display element, and including a plural number of projection lenses therein; and a reflection mirror for reflecting lights emitting from said lens group, to be projected onto said projection surface, obliquely, wherein assuming that a light beam, emitting from a center of the display screen of said image display element, passing through a center of an entrance pupil of said lens group, and entering into a screen center on said projection surface, is a screen center light beam, then said screen center light beam is incident upon said projection surface, obliquely, with respect to a normal line thereon, said lens group comprises a front lens group including a plural number of refraction lenses, being disposed thereafter directing from said image display element to said projection surface and having rotationally symmetric surface configurations, and a rear lens group including a refraction lens having a negative power and having a rotationally symmetric surface configuration and a plural number of lenses having rotationally asymmetric free curved surface configurations, and within said rear lens group, said lens having the negative power is movable in an optical axis direction, and at least one piece among said lenses having the free curved surface configurations is movable into directions, including the optical axis and direction perpendicular thereto, within a surface including the optical axis and the normal line on said screen.