Page:Popular Science Monthly Volume 89.djvu/785

 Popular Science Monthli/

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��lens-board in or out. Remove the slide and adjust the arc-hini[) to remove the bluish spots that will most likely be seen in the field of light. By moving the lamp up or down, to the right or left, or

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��Fig. 12. Dimensions of the upright which serves to carry the light-shield

back and forth upon the tubes, the field will gradually be made perfectly clear. When the light is uniformly white, the slide may be replaced and a sharp focus obtained by turning the milled, adjusting knob on the lens-barrel. All lenses

��should be ket scrupulously clean, since the slightest trace of dust will diminish the brilliancy of the illumination to an astonishing degree.

Lantern-slide plates may be oblainerl from any dealer in photographic ma- terials. The standard size is t,}4 in. by 4 in. in the United States, and all slide- carriers made for use in this country take that size. The lantern slide emul- sion or coating is so sensitive that the slides must be han- dled under ruby or deep orange light only, in order to avoid fogging. With this one ex- ception, they ma>- be handled precise- ly as one would use the popular devel- oping-out papers.

To make the slide, the plate is placed in a print- ing-frame, with its emulsion (dull) surface next to that

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���Fig. 13. The light shield which is sol- dered to the upright

��of the film or plate from which the print is to be made. The frame is then held at a distance of about 6 ft. from a 25-watt tungsten lamp, and the latter turned on for two seconds. This exposure is correct for the average negative and is cited merely

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��Fig. 14. Details of the arc-lamp which is adapted for use on comparatively small currents. The carbons are fed by merely twisting and pushing the knobs fitted to their ends

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