Projection Apparatus (1917)

Bausch & Lomb Optical Company As there are many occasions when objects of considerable thickness, such as pieces of apparatus, anatomical specimens and the like, will be placed on the object holder, a cam actuated by a lever has been fixed to the support so that the object holder can be quickly lowered and left in fixed position at any point, thus bringing the upper surface of the object to a level with the bottom of the dark chamber for easy focusing, Figure 3. When at the lowest point of this adjust- ment, the object holder is 6 inches below the floor of the dark chamber. The plane of illumination, and therefore its intensity on the object, is the same for all distances from the screen as focusing is accomplished by moving the projection lens to and from the object. For the convenient projection of post cards and small prints we supply with each outfit a frame and two adjustable holders. The frame fits over the opening in the bottom of the dark chamber, and the holders are very easily manipulated. The new Convertible has a maximum opening in the bottom of the dark chamber of 8x10^ inches. This opening is intended for use only when placing large trays containing anatomical specimens, etc., in position. When projecting cuts, diagrams and the like, an area 8 inches square is the largest we recommend, and we provide a diaphragm with such an opening to fit into a slot in the bottom of the dark chamber. As it is often desired to project illustrations and objects of smaller sizes than this, we furnish with each outfit two other diaphragms with square openings of 6 inches and 4 inches, respectively. The first two lenses of the triple condensing system are mounted directly in front of the lamp house and constitute a suitable system for projection of opaque objects, giving a beam of light in the dark chamber of sufficient diameter to cover the large area to be projected. When using smaller areas, the arc lamp can be drawn away from the condensing system so that the beam of light just covers the area to be projected. This means increased illumination, since the same quantity of light is spread over a smaller area. The adjustment of the arc to and from the condensers is easily controlled from the exterior of the lamp house. It is only necessary to loosen the clamping screw at the bottom of the lamp house and shift the lamp backward or forward by adjusting rods at the rear. For opaque object projection we offer four different projection lenses for use on this instrument. Their corrections for astigmatism and flatness of field are superior to anything heretofore produced for the purpose. Three of these lenses are of the same construction and have focal lengths of 15, 18 and 25 inches, with a corresponding ratio between aperture and focus of F:4.0, F:4.8 and F:5.0, respectively. The fourth lens is one of 15-inch focus, with a ratio between aperture and focus of F:3.5, so that this lens has the greatest light transmitting power of any, while its covering power leaves nothing to be desired so far as flatness of field and definition are concerned. All of these lenses, with the exception of the 25-inch focus, are mounted on the top of the dark chamber in a vertical position. A reversing mirror is carried over the front of the lens on a separate support. The mirror is silvered on the first surface, giving the nearest approach to a totally reflecting medium that can 72