Illustrated Catalogue Of Magic Lanterns (after November 1889, probably 1890)

58 MCINTOSH BATTERY AND OPTICAL CO., CHICAGO, ILL., U. S. A. PROJECTION LENSES. Achromatic Objectives for Lanterns. The most desirable feature to be looked for in a Lantern Ob- jective is its defining power; it is not difficult to obtain an objec- tive of any desired magnifying power—what is wanted is a clear, sharp definition, a flat field brilliantly illuminated to the very edge of disc. There are many different makes of objectives on the market, but only a few are worthy of your attention. The best Lenses are the Darlot, Voigtlander, Dalmeyer, and Suter. We prefer the Darlot, taking everything into consideration, as the best Lens made for general work. These Lenses are mounted in finely finished and lacquered brass, and have the highest grade rack and pinion action. There are different sizes of Objectives, that are known as “One-Fourth,” “One-Third,” One-Half,” “Two-Thirds,” and “Four Four” sizes. While this nomencla- ture is arbitrary, and the same size lenses by different makers have different powers, yet the law of each lens is a fixed one—at a given distance will make a certain size of picture. This law cannot be changed. The law of the different Darlot Lenses is as follows: A “One-Fourth” makes a disc, or picture, in diameter or square one-half its range. A “One-Third” Lens makes a disc, or picture, in diameter or square one-third its range. A One-Half Lens makes a disc, or picture, in diameter or square one-third its range, less io per cent. A “Two-Third ’ Lens makes a disc, or picture, in diameter or square one fourth its range, plus io per cent. A “Four Four” Lens makes a disc, or picture, in diameter or square one-sixth its range, minus io per cent.