The optical lantern is a device for showing an enlarged repro duction of a small picture upon a screen before an audience. The small picture from which the projection is made is most conveniently a transparent picture, formed photographically upon glass by photo graphic processes. Modifications oi the lantern may be made to Show pictures upon opaque surfaces, such as newspaper clippings or souvenir postcards, or may Show projections from solid objects. Still another modification of the optical lantern is that in which the motion head with its strip of pictures is substituted for the fixed slide in its carrier, and motion pictures are shown upon the screen. The lantern consists primarily of a lamp for lighting the slide and a system of lenses for focusing the slide upon the distant picture screen. A slide holder is provided for receiving the slide and is adapted to hold it in position in the lens and lamp system. A lamp house is provided for the lamp, obscuring all light except that which passes from the lamp through the slide and through the lens system. The lens system usually is divided, one part being placed between the lamp and the slide, and the other part being placed between the slide and the picture screen upon which the image of the slide is to be projected The lenses between the lamp and the slide are called the condensers, and the lenses between the slide and the picture screen are called the objective lenses, or more brieﬂy, the lens.