The Optical Magic Lantern Journal (February 1894)

The Optical Magic Lantern Journal and Photographic Enlarger. 25 Claudet stated that he himself had tried to solve the problem, but so far the results were imperfect. In The British Journal of Photography for 1865 is a diagram and description of a stereocsope, invented some years previously by Mr. Colman Sellers, and the accompanying simplified diagram, Fig. 1, will serve to explain the construction. An axis, carrying six vanes, was made to rotate inside a double drum; the stereograms were fixed at the places marked a, and were viewed through the stereoscope k. Outside these wings, or vanes, was a circular band of tin, not represented in the diagram, in which band slits were cut at intervals, and through the slits the pictures could be seen at the proper moments, to give the appearance of motion to the object, as in the ordinary thaumatrope or ‘‘wonder worker.” Thaumatrope seems to be the best of the names of the ordinary instrument, which has several aliases, such as phantasmacope, phenakistiscope, and So On. With single pictures, Anschutz of Lissa has recently produced fine lantern thaumascopic effects by mounting the slides on the circumference of a large revolving ‘iisc, and illuminating each one with a brilliant electric discharge whenever the slide reached its proper place between the condenser and the projection lens. Possibly there are no great difficulties in mounting stereoscopic slides in the sane way, and illuminating them by a flash of light at the proper monient; the flashes perhaps might be given by the lime or other lantern light, by means of a second revolving wheel, pierced with holes at the proper places. A fault in some English and American thaumatropic lantern displays ‘has been, that the pictures have been too few in number to pleasingly represent a given motion. Anschutz has avoided this defect, so that delicate undulating motions of the muscles and hairs of animals have been smoothly represented. In taking photographs for the stereoscope, the distance apart of the lenses should depend upon the distance from the camera of the nearest somewhat prominent object in the foreground. If then a camera were placed on the side of a mountain valley, with no foreground within one or two miles, and that a village perched on the opposite side of the valley, what is the best way to get stereoscopic effect? The late Mr. Donkin, who lost his life in the exploration of the Caucasus, used simply to take two negatives with an ordinary camera, suitably shifting the position of the stand between each. Many will remember Mr. Latimer Clark's early stereoscopic camera, in which the camera was made to slide along a board, so that one view could be taken from one end of the board, and the other from the other end. Not so many perhaps have heard of the instrument devised by Helmholtz to gain a stereoscopic effect in viewing distant objects, by an optical arrangement yielding the same results as if the eyes were farther apart—say a yard apart—and the principle of which instrument apparently might be modified and adapted to taking binocular views with twin telephotographic lenses. Fig. 2 will explain the principle. Let KK be two reflecting plane mirrors, and Aa prisin; the eyes of the observer, ww, will then see a distant object, as if his eyes were, say,a yard apart, at HH, and looking in the direction aN. A photographic adaption of this principle then, might perhaps be devised to get stereoscopic views of distant objects for the lantern stereotrope, or other purpose required. While dealing with these curious old instruments, it may be as well to draw attention to the modification of the stereoscope devised by Clerk Maxwell, and brought by him under the notice of the British Association at Dundee, in 1867. It consisted of a baseboard, asc, about two feet long, with an ordinary stereoscopic picture, A, at one end, and two small twin lenses at B; these lenses were each of six inches focal length, and their centres about one and a quarter inch apart; their support had a sliding motion along the board for adjustment. Atc was a frame carrying a lens three inches in diameter, and of about eight inches focal length. The effect is that the observer sees a real instead of a virtual optical image, looking like a real object in the air close to the large lens. :0: Home made yv. Commercial Lantern Plates. By Lewis Mepuanpb. Mr. Crirron in his article on the Hill-Norris plate states, ‘(that even the most devoted advocates of the collodio-bromide process have, almost without exception, dropped it in favour of commercial gelatine plates.’’ A few words from an ‘ exception” may prove of some interest. There are three principal reasons why this ‘process "' has been deserted by so many, viz.. the difficulty of procuring a suitable sample of pyroxiline, a reasonable quantity of methylated spirit (free from mineral naptha), and the trouble attached to the manufacture of the emulsion.