Patent ID: 6880937

Claim:
A projection optical system for projecting an image displayed on a predetermined display surface onto a predetermined projection surface comprising: a front lens unit situated on the projection surface side; a rear lens unit situated on the display surface side; a first decentering lens unit situated between the front lens unit and the rear lens unit, movable in a direction perpendicular to an optical axis of the projection optical system; a second decentering lens unit situated between the front lens unit and the rear lens unit, movable in a direction perpendicular to an optical axis of the projection optical system and substantially perpendicular to a direction where the first decentering lens unit is moved; and a driving mechanism for continuously reciprocating the first and second decentering lens units in directions perpendicular to the optical axis, wherein the projected image on the projection surface is periodically shifted by reciprocating the first and second decentering lens units, and wherein the following conditions are fulfilled: 0.01 ≦|FR/FD 1 |≦0.2, and 0.01 ≦|FR/FD 2 |≦0.2, where FD 1 represents a focal length of the first decentering lens unit, FD 2 represents a focal length of the second decentering lens unit, and FR represents a focal length of the rear lens unit.