Motography (Jan-Jun 1915)

March 27, 1915. MOTOGRAPHY 479 Fundamental Principles TRANSFORMED BY FEATHERSTONE PROJECTING THE PICTURES. AFTER the "positive prints" have been made from the negatives by means of either of the printing operations just described, or, in rare cases, by the "optical method" to be described later, they are developed, washed and dried, and are then ready for "projection." The developing and washing used to be a very tedious operation, and even now some manufacturers wind the films on racks or large drums which must be handled many times during the various processes, but as in other branches of this young and overgrown industry, there are indications that really scientific methods will supplant the clumsy makeshifts that were plenty good enough before quality was considered. AUTOMATIC DEVELOPMENT. Automatic machinery for printing, developing, fixing, washing and drying is now available, and soon all of the best plants will have the modern equipment, which will be described a little later on. This will not only save much time and labor, but will remove many of the annoying defects in the projected pictures. Everyone has noticed that when looking at some pictures on the screen, there will be occasional flashes of light, usually occurring regularly about every three or six seconds, but sometimes more often and irregularly. These flashes are caused by "thin" places in the positive film, which in turn were caused by "dense" places in the and drums shall have given way to the continuous automatic machines. THE CAUSE OF LIGHT FLASHES. Just how these occasional dense and thin places are caused is very interesting, especially on account of the lessons which may be learned as to the extreme delicacy of the developing operation. When films are developed according to the rack method they are wound on racks or frames which usually hold either 200 or 400 feet, and in their simplest form are made of four sticks about 4 feet long, two of them being round, and held about four feet apart by the other two. The film is wound about the round sticks in 25 turns or laps of 8 feet each, for a 200 foot rack, and then this Figure 20. Threading the film. A modern projector. negative. The effect is often complicated by occasional dense places in the positive, and they are mostly due to uneven development, which will not occur when all racks loaded rack is put edgeways down into a developing tank along with several other racks. EFFECT OF TEMPERATURE ON DEVELOPMENT. Now suppose that the proper temperature for development is 65°, then if it should be warmer the development would proceed too rapidly, and if colder it would be too slow. Similarly if a portion of the developer or a part of the film should be warmer, then the development of that part would be more rapid than other parts, and it would come out of the bath more dense. Well, this is exactly what happens to 90% of the films made today, but frequently it is unnoticeable or almost so, and it is customary to overlook it as a minor fault. Theoretically, it will not occur ;'/ the temperature of the developing bath, and the temperature of the rack are exactly the same, but this is rarely the case. Hence, when a rack at temperature 70° is immersed with its load of film into a bath at temperature 65° the film that does not touch the rack will quickly take the temperature of the bath, while the film that touches thesticks as it turns about either end of the rack will be kept at a higher temperature for .at least several seconds, or plenty iong enough to give it a big start in development. Nothing that can now be done will "even up" the density, as the early stages of development are the critical ones, hence there will be a darker place on the film at each turn, or about 4 feet apart. If this happens to be a negative film the defect will be passed on to the positive, but will be reversed, and the dark part of the negative becomes a light place on the positive, and when projected on the screen, there will of course be a flash of light every time a thin place comes along. This would occur every 3 or 4 seconds if the rack had the above dimensions, for pictures are usually run about 20 per second, and as there are 16 to each foot of film, the actual "travel" of the film through the projection machine would be 1% feet per second, making