Projection Apparatus (1917)

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Bausch & Lo m b Optical Company Ealer, the great Swiss mathematician, recognized its possibilities more than a century ago but was prevented from developing them by an utter lack of efficient illuminants. Sunlight was about the only form which was sufficiently bright, and that was impracticable for projection purposes. Thus the modern achievements already alluded to may be attributed to the development of illuminants as well as There are six applications of optical projection available to- Six Different day _ pro j e ction of lantern slides, of opaque objects, of micro- Applications objectSj of horizontally placed objects by transmitted light. projection with polarized light and projection of the spectrum. In our various equipments we provide for all six of these applications in a thoroughly practical and efficient manner. Lantern Slide Projection This is the primary form of projection. It is effected by sending light from a suitable source through a set of condensing lenses, which serve to direct the rays in even distribution through every part of the transparent glass slide bearing the object to be projected and then through the projection lens, or objective, which casts the enlarged image on the screen. S Path of Light in Lantern Slide Projection. The arrangement of parts is indicated in the accompanying diagram, in which E is the ilium inant, C the condensing system, D the slide, O the diaphragm plane of the objective, or projection lens, and S the screen. Projection of Opaque Objects The projection of opaque objects, such as post cards, photographs, book illustrations, type matter, maps, drawings and even solid objects, is one of the latest forms of projection to be developed to a truly high standard of efficiency. It has become very popular, however, among educators and all users of projection, since an almost unlimited amount of illustrative material is thus rendered immedi- ately available for the purpose at a very low cost. 7