The Moving Picture World (1907)

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THE MOVING PICTURE WORLD. Animated Photography: The Prin- ciples and Advantages of Duplex Projection. A Lecture Delivered Before the Royal Photographic Society of London. By Robert Thorn Haines. (Continued from last week) It would seem impossible, by any known means, to ob- tain one continuous picture of moving objects, necessitat- ing one continual exposure, resulting in a blur; but for practical purposes, all that is necessary is to photograph the movements by a series of successive exposures, pro- ducing a series of separate photographs of the successive phases of the movements, taken at such short intervals as do not allow the objects during the interval to move further than the distance between any two points which would cause them to appear as distinctly visible phases of the movement, at the range from which the photographs are taken. It is imperative, in order to attain the same speed of movement of the objects, that they be exhibited or shown at the same rate as they were taken. According to the law of persistence, the longer the duration of image the longer it continues to remain upon the retina, and there,can be no doubt about this being due to the fact that the image takes as long to gradually im- press itself upon the retina as it takes to fade away. It will be readily understood, therefore, why it is that the faster the objects are travelling the greater the number of impressions which must be taken, not alone to secure a complete analysis of the movements, but to ensure the individual pictures of the series being taken at such a speed as will enable them to be projected within the limit of persistence, when the same number per second are ex- hibited as were taken. If an insufficient number of pictures be taken and pro- jected in a given time to satisfy these conditions, the distinct differences between the pictures will be visible and show a disjointed instead of a smooth continuous movement. The principal object I aimed at in my ex- periments was not to provide a means for producing stereoscopic effect, nor yet to produce the pictures in natural colors, but to consummate the first essential of the ideal by devising a means of - reproducing the moving objects naturally and continuously, without any break, interval or interruption. I realized that whatever means I adopted for remedy- ing the defects, it would be absolutely essential to arrange the projections so that one picture wo^uld always be sta- tionary on the screen. But as the pictures must neces-* sarily be successively changed, it was obvious that if the film be moved continuously some means should be em- ployed for rendering it optically stationary. This could be done by a system of prisms and mirrors or moving lenses, but none of these methods appealed to us as being thoroughly practicable, or likely to produce satisfactory results. I concluded that the only practicable method was ti separate the positives in two alternate series^and \ rojĀ« them separately through two optical systems 'to a .oind dent position on the screen; but again there ap jean two Uternative methods of doing this. I first tl on that it might be possible to print the pictures in -uch manner that the film could be kept continuously moving, and have the two projection lenses arranged to movs also relative to it, so that the centers of the pictures wouli pass through the centers of the lenses and always rem optically stationary in alternation and coincide. Thii method I decided was impracticable, owing to the neo sarily complicated movements, and to the impossibility ol moving lenses, which would necessarily be heavy, at required speed, without introducing such an amount 4 instrumental vibration* as would be detrimental, if nci fatal, to the result. The other alternative and only remaining system which I decided was practicable, was first to : take the pictures from one point of vfew and^by a special printing machine, separate them in two alternate series so that the suo sive pictures of each series could be projected alternatel through two fixed lenses. This system obviously enabli one picture to remain stationary and projected, while picture which has just been shown is removed and tk| next in succession placed in position, and also enables] the two series of pictures to remain stationary during i portion of Che period of operation. If the successive pictures of these two series be correctly superimposed; by the two projection lenses, and translated so that eacfcj picture in succession alternately remains stationary whiM the other is removed, and if for a period the film or fi!m^ containing these two pictures be kept -stationary wl one is obscured in the same ratio that the other is sho' the screen will be continuously occupied by a complefe! picture, and flickering obviously done away with. For the purposes of my first experiment I had a s set of machines constructed, consisting of a perforator, printer, camera and projector. On account of the sic movement of the mechanism, which enables large filtK] to be used with as great a facility as those of the ordinal standard gauge, in the machines I elected to employ tv positive films, having pictures four times the area of ordinary standard gauge, printed by the special prints machine alternately in two successive "odd" and "even' i series upon them. Each pair of these positives wt printed from one film containing the full original negatii series of pictures. The printing machine -brought positive pictures together without leaving any bl spaces between them, so that the area of the two posi films was exactly equal to the area of the negative. The duplex-projecting system comprised a sprocki and special reciprocating beater mechanism, fitted innumerable adjustments required for regulating adjusting the films, lenses, etc. The pictures on the separate films were alternately translated past each of projection lenses of the instrument, which were pk' horizontally about 7 inches apart, and were projected