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Bausch & Lomb Optical Company c Figure 2—Application of Kohler Illuminating System to Model D Balopticon. „ ... In adapting this illuminating scheme to our model D Balop- Our Illuminating Systems ticon we have substituted for the single condensing lens, C in Figure 1, our triple condensing system (see Figure 2). This change of condensers was made to enable a quick interchange between microscopical and lantern slide projection. We furnish a substage condenser of a suitable numerical aperture and optical construction to meet the special requirements. The regular Abbe condenser is not suited to this purpose because of its short focal length. In the case of our Universal Balopticon the large projection lens for opaque objects, supplemented by a special condensing lens, is substituted for the front lens of the triple condensing system. Figure 3—Application of Kohler Illuminating System to Convertible Balopticon. Still another adaptation of the Kohler system is now used to give the excep- tional results possible with the Convertible Balopticon, especially in higher power work. The path of light is shown in Figure 3. To obtain this the condensing lens directly back of the lantern slide carrier, which lens is mounted in a swinging arm, is thrown out of the optical axis, and a small double convex lens, mounted in the dark chamber, is swung into position directly in front of the large rear condensers. This produces a gradually converging pencil of light, which finally forms a large image of the arc at the diaphragm plane of the substage condensers and fully fills the aperture of the high power condenser. With the improved substage condensers this arrangement is used for all the different powers of objectives that may be required. An important consideration in selecting apparatus for micro- Magnifications sco P' ca l work is the optical equipment required to obtain the desired magnifications. The following table will be found of value. It gives the approximate magnifications obtained at different projection distances with the objective alone and with the objective combined with our 3X or our 5X projection eyepieces (see “Accessories”). The projection distances given are 11