Abstract: An optical apparatus, e.g. a foldable overhead projector of the reflection type, includes a base table, whereon original material is placed on a Fresnel mirror. A projector head forms an image of the original material. A stand is swung on the base table. The stand, when folded, overlies a control portion of the Fresnel mirror. The projector head is vertically swingable on a distal end of the stand. A stand locking lid is swingably mounted on the stand distal end. Retaining claws are formed at a front of the locking lid. Receiving recesses in the base table retain the retaining claws, and keep the stand folded. The locking lid has a manually pullable edge, which is pulled to disengage the retaining claws from the receiving recesses. The projector is thus erected and folded easily, because it is openable quickly for erection.

Abstract: A variable power reflectory type overhead projector for forming a projected luminous beam by lighting a reflecting mirror from the projecting lens side. A transparent film-to-be-projected support is provided between a regular position of the film to be projected and the projecting lens, and an auxiliary lens is included for focusing the projecting lens on the support.

Abstract: An overhead projector having a stationary main body including a Fresnel plate, a projection unit, and a swingable member for supporting the projection unit and swingably secured to the main body. The overhead projector comprises one way clutch means through which the swingable member is secured to the main body and which is adapted to limit the swinging motion of the swingable member towards the main body.

Abstract: A portable overhead projector wherein characters, a picture and the like drawn on a transparent sheet rested on a horizontally supported stage can be projected onto a screen or the like, and having a safety device in which a projection unit can avoid impinging upon a mirror-Fresnel plate, thereby preventing damage to it. This safety device features a lock mechanism for preventing projection unit supports from rotating unless the projection unit is folded toward the supports. Furthermore, the overhead projector has a rotatable support for one side of the mirror-Fresnel plate whereby the mirror-Fresnel plate is held horizontally during projection, and is inclined during housing, whereby the projection unit is housed in a space formed by the inclining of the mirror-Fresnel plate.