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Bausch & Lomb Optical Company / / Figure 2—Diagram Showing Path of Light for Lantern Slide Projection: A = Arc; B - - Rear Lenses of Condensing System; C = Front Lens of Condensing System; H = Projection Lens for Lantern Slides; M = Optical Bed; N = Slide Carrier Holder; 0 = Bellows. in 4x5 or 5 x 7-inch sizes. For these we have arranged a special set of lantern slide accessories with an 8-inch diameter condenser which fully illuminates these large sizes. Projection of Opaque Objects Appreciating the growing importance of the projection of opaque objects and illustrations in educational work, our Technical Bureau has made this type of projection a special feature of the Convertible Balopticon. The lamp house is inclined, as shown in Figure 3, and an exceptionally brilliant image of the object is obtained since this arrangement gives the maximum illumination obtainable from a single light source. The light source is brought as close to the object as is practicable, and the light is thrown directly onto the object. The path of the light is shown in Figure 4. There is only one mirror reflection, by which the light is directed toward the screen and the image caused, at the same time, to appear in correct position from left to right on the screen. The lamp house is easily tilted as shown and held rigidly in place by a strong spring arm. A wide range of opaque material can be utilized with this instrument. The object is always held in a horizontal position, and the design of the base and object holder is such as to permit materials of greatly varying size and shape to be projected. To prevent light from escaping into the room when large objects are being projected the Convertible is supplied with velvet curtains suspended from the bottom of the dark chamber on either side of the base. A metal shield at the front of the base prevents the screen from being flooded with light when changing objects. The curtains are hung on rods and can be slid out of the way or entirely removed when not in use. 70