A light beam projector includes a shell; a light source; an outlet lens; a first optical body for focusing a light beam from the light source, interposed between the light source and the outlet lens; a second optical body for varying the focal length of the light beam, interposed between the first optical body and the outlet lens; a third optical body generating an optical effect on the light beam; the third optical body including a lens movable between a non-operating position and an operating position, wherein the third optical body is positioned along the light beam trajectory; a carriage for supporting the third optical body; and a movement device connected to the carriage for moving the third optical body along a trajectory parallel to the shell so as to modify its position relative to the first and second optical bodies.