Abstract: An overhead projector of the under mirror type includes a projection head assembly supported on a column so as to be located over a stage on the top of a housing and so as to be pivotable between a standing position and a stowed position. A projection lens is fixed on a lens frame and a reflecting mirror is fixed on a mirror plate. Both the lens frame and the mirror plate are rotatably mounted on a single shaft further mounted on the head body of the projection head assembly so that angles of the lens and the mirror are increased and decreased. The lens frame is rotated by a self-weight of the lens in such a direction that the angle of the lens is decreased, when the projection head assembly assumes the standing position. A link lever interconnects the lens frame and the mirror plate so that the angles of them are adjusted so that the angle of the lens doubles that of the mirror. A mirror locking element locks the mirror at a position where the angle of the mirror is maximum.

Abstract: An overhead projector includes a housing including a stage which is formed in its top wall and on which a transparency bearing an image to be projected is placed and an air outlet formed in one of its two side walls, an exhaust fan incorporated in the housing for exhausting air in the housing through the air outlet of the housing, a projection light source such as a high illuminance halogen lamp disposed in the housing for illuminating the transparency on the stage from inside the housing, a projection head mounted for projecting a magnified image from the transparency on a screen and including a focusing lens and a reflecting mirror, a column mounted on the housing to hold the projection head over the stage, a Fresnel lens disposed inside the stage to converge light from the light source on the focusing lens of the projection head, a cooling fan, and air guides for guiding air delivered from the cooling fan so that the air flows along a surface of the stage.