Optic projection : principles, installation and use of the magic lantern, projection microscope, reflecting lantern, moving picture machine (1914)

242 BLACK APPARATUS FOR MICRO-PROJECTION [Cn. IX eter into the center of which is screwed the objective (fig. 138), then the field is not at all restricted. The low power objectives can be focused easily by moving their supports back and forth along the optical bench by hand (fig. 158-159). FIG. 136. MECHANICAL STAGE OF WIDE RANGE. (Cut loaned by the Bausch & Lomb Optical Co.}. This mechanical stage can be attached to any microscope with square stage, and it permits the use of large slides. The right to left scale is 80 mm. and the front to back one 58 mm. The actual range available depends on the size of the stage of the microscope. BLACKENED APPARATUS § 370. The light necessary for micro-projection is so dazzling that it should be kept strictly within the projection apparatus by means of a proper lamp-house and bellows, so that the only light which finally reaches the screen is that which passes through the projection objective. But this ideal condition cannot be wholly realized in practice, hence the necessity of making the outside of the entire apparatus, from lamp-house to microscope tube, dull black. Then any escaping light will not be reflected from polished surfaces and scatter light into the room, on the one hand, or blind the eyes of the operator and annoy the auditors on the other. Projection apparatus found in institutions, in many cases, have a finish of polished brass or nickel. If the operator cannot focus