Motion Picture News (Jul-Aug 1916)

July 15, 1916 ACCESSORY NEWS SECTION 305 looking at a photographed result lying in bhe plane— either a print on paper or projection on a flat surface or screen — and the eye remains fixed in its focus while viewing the same. In other words, in stereoscopy all of the objects in view, regardless of their relative distance in nature, are reduced to one plane in the photographic result. The various objects — reduced to one plane in the print — are also fixed and unalterable in focal value, while upon the retina of the eye they are reduced to one plane but with alterable focal value. By reason of these facts a dissimilar pair (or series of pairs) of photographs when viewed in a stereoscope exercise the axes of the eyes artificially in the same way as would be the case when looking at the objects in nature. Although efforts were made by Elliot as early as the year 1834 to pro'duce a suitable device for viewing pictures made with stereoscopic relation to each other, it was not until August, 1838, that the first practical stereoscope was brought out by Professor Wheatstone, and exhibited by him before the British Association at Newcastle. The principle on which the Wheatstone stereoscope worked is diagrammatically shown by Fig. 1, in which. A, A are the two holes to be looked through, B, B are the two pictures or photographs (having stereoscopic relationship to each other) and C, C are two mirrors which reflect the two pictures toward the observation holes or eyepieces. Although the Wheatstone Stereoscope marked a notable advance in stereoscopy its performance was faulty in several respects. One defect was its reversal of the picture being viewed — thus if a view contained lettering, the words would appear backwards. Another fault was double reflection unless special mirrors, burnished on the surface were employed. Having given these deficiencies of the Wheatstone instrument his serious consideration, Sir David Brewster set about to design a more perfect instrument, and the result was his Lenticular stereoscope, which embodies the principle employed in the presentday stereoscopes. The Lenticular stereoscope employs the principle of refraction instead of reflection and in addition to effecting the coalescence of the dissimilar pictures they are also improved by being seen magnified. Two convex prisms are utilized in the Lenticular stereoscope and the action of the instrument is shown in Fig. 2. In Fig. 2, A, A are the eyes of the observer, B, B are two convex prisms, while C, C and D, D are the two pictures (mounted side by side) which are being examined. The convex prisms refract the light emanating from the pictures, and the eyes see their respective pictures properly combined, and (as before noted) magnified. Originally the Lenticular stereoscope was of boxed-in form, the pictures being inserted at the top after opening a little door thereon. But the stereoscope as we now know it — with its hood for the eyes, its frame for holding the pictures (adjustable as to distance from the lenses) and its folding handle — was designed by the wellknown American poet, Oliver Wendell Holmes. It is on the lenticular principle, however, employing the, same convex prisms as the Brewster instrument. In some of the best modern stereoscopes there is means provided for varying the refractive angle, which is accomplished by increasing or decreasing the separation between the eyepieces or convex prisms. This adjustment is found useful at times to accommodate persons whose eyes ar.e abnormally separated from each other. Having reviewed the methods of examining stereoscopic pictures, the cameras for securing pictures or series of pictures possessing stereoscopic relationship will next be considered. Two separate cameras may be employed to secure the negatives, and when this is done the axes of the lenses may be directed toward the subject' in such a way as to secure the very best effect. If of good design and accurate construction, however, the customary double or stereoscopic camera may be employed with excellent results. Lenses for stereo work should embrace a medium angle of view and should be very accurately paired or matched, with regard to identical focal length, defining quality, and speed, the latter condition not being so important as the first two mentioned. Means should always be incorporated, in the case of double cameras, for increasing or decreasing the separation of the lenses. For a subject close at hand the lenses must be brought closer together, while for a distant subject the lenses are separated more, the normal distance between the lenses being ahout lYi inches. Tliese conditions are in accordance with the action of the eyes as detailed in the earlier , part pf this article'. , 'Jo ; jri /. :'; "EASTMAN 55 in the film margin answers the question, "How clear should a motion picture beV EASTMAN KODAK CO., ROCHESTER, N. Y. Universal Camera For Motion Photography Write for Illustrated Catalogue ""^^'r^^'oIV^Tin-n * ri007 Times Bldg., New York The UNIVERSAL CAMERA CO. Branches-^ 821 Market St., San Francisco 559 W. Jackson Blvd., Chicago L 229 E. Sixth St., Los Angeles Perfect Developing and Printing TITLES in any language Sc. Negatives Developed . Ic ft. Positive Printing .... 4c. ft. 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