Motion Picture News (Oct - Dec 1928)

1830 Motion P i c t ii r e N e w s Projection /% Optics, Electricity, Practical Ideas & Advice Inquiries and Comments Film Buckling Responsible for Shutter Clwnges SATISFACTORY solution to the film buckling problem seems to have been reached at last. It involves simply a change in the location of the revolving shutter from its former position in front of the projection lens to a place immediatel.v behind the aperture. In this new position the shutter is double acting in that it serves to mask the light beam (its primary function) and at the same time shields the film from the radiated heat within the beam during the light washing period. Thus, bj simply changing the position of one element in the projector optical system a defect is satisfactorily corrected, the eftieiency of the system is maintained at its normal value, and complicated mechanisms for cooling the film are avoided thus retaining simplicity of design. In Step with Progress Placing the revolving shutter behind the aperture constitutes an improvement which is directly in line with new developments in the art of motion jiicture projection. By the same token it is indicative of the alertness ■of projector manufacturers to the ever oc•curring changes with which tlie industry is faced. The matter of film buckling has been a serious one ever since the introduction of the reflector arcs. This system, with its greatly increased efficiency in light transmission subjects the film to heat levels W'hich are higher than those encountered with the old condenser forms of optical system-s. There is an axiom in the lighting field that light and heat go hand in hand and any increase in the foraier is attended by a like increase in the latter and vice versa. This seems perfectly logical in view of the fact that heat, too, is a wave motion and is subject to the same control by means of lenses, prisms and mirrors. Early Attempts at High Cooling Efforts have been made at various times to protect the film from excessive heating in the new fornus of illuminatoi's but the principal result was merely the evolution of cumbersome forms of cooling devices which found no permanent place in the projector optical system. Forced draft devices which drew a stream of cold air past the aperture or played a stream of cold air directly on the film were frequently tried but were generally unsatisfactory. Aside from being cumbersome, these devices were inefflcient and approached the problem from the negative standpoint in that they all first permitted the film to be lieated and then attempted to dissipate this heat stored up in the film. This was equivalent to evolving a method for finding a horse which had been stolen instead of taking the more direct method of preventing the horse from being stolen in the first place. Placing the revolving shutter at the aperture location prcz'Ciits the film from being excessively heated and so takes the forni of a preventive rather than a cure. This method is infinitely better. Why Film. Buckles The best opinions on the subject ascribe the buckling of film to its lack of perfect drying. Film which leaves the laboratory imperfectly dried will be subjected to a violent drying operation as it passes the aperture during the coiirse of projection and it is this almost instantaneous drying during projection which sets up uneven strains in the film and causes it to assume shapes other than that of a perfectly fiat ribbon. More specifically, the action is claimed to be as follows : Imperfectly dried film passing through the projector during projection is subjected to a preliminary heating before it reaches the aperture from its contact with the heated mechanism. The edges of the film, being in direct contact with the sprockets, guides and tension springs are heated more than the center strip of the film which rides practically free. Some degree of strain is thus established due to this preliminary uneven heating. As the film is exposed to the beam passing through the aperture, the center strip of film, which until now has been little heated, is suddenly subjected to a large increase in temperature whereas the edges of the film are protected from direct exposure to the projected light beam. A violent strain is then established in the opposite direction. The net result is that the center portion of the film not only tends to, but actually does, expand more than edges and this unequal expansion gives rise to the so-called l)uokling. Its Effect on Projection The effects of buckled film are evidenced during projection by the projectionists inability to keep an entirely sharp defined picture on the screen. The film, as it passes, the aperture, does not present a flat plane to the projection lens but on the contrary presents different planes which vary in their distances from the lens. Focussing the lens, therefore, for the normal position of a fiat film at the aperture is inqjossible as the film constantly changes its position. In extreme cases, it is not at all uncommon for the projectionist to remain at the working projector and continually refocus the lens in order to keep a legible pictui'e on the screen. Such a procedure, of course, is absurd even if it were effective, but no matter how alei't the projectionist may be to catch these changes the definition of the picture is certain to be affected. It might logically be asked that if imperfect drying of the film is responsible for its buckling then why not eliminate this trouble at the source by correctly drying the film. It is far easier and simjiler to find a universal preventive for buckling than to try to obtain the cooperation of a large body of companies who may or may not be in favor of going to the extra work required to perfectly condition their product which they consider to be at best, but temporary. It seems almost certain that the old type of revolving shutter placed in front of tlie projection lens is doomed to extinction. In view of the fact that the old shutter location possesses no marked advantages as compared with the new one, its disappearance should be no cause for grief. The aperture-shutter, on the other hand, holds forth sharply defined pictures, the conservation of film and projector parts, and a lessening of the projectionists duties in that he is not required to devote much of his time to watching the screen for its definition. Two Florida Theatres Acquired by Publix Plans are being rushed by the Publix Theatre Corporation for the opening of the Polk theatre, at Lakeland, Fla., which was erected during the time of the Florida boom, of Spanish atmospheric style, and at a cost reported to be close to a million dollars. The name of the Polk, which seats 2,000 has been changed to Rio. Recently final deals were closed between the owners and Publix, whereby the Polk and another theatre never before opened, the Lakeland, were purchased outright by Publix. It is the plan of the company to open the Polk (now the Rio) some time in December with Movietone and Vitaphone. The Lakeland will open its doors the early part of next year, also with sound. Representatives of Publix' maintenance departments in Atlanta and New York are at Lakeland now, rushing through the equipping of the new Rio. All furniture, etc., will be in keeping with the Spanish style of the house. The Rio policy will be sound at popular prices, and the Lakeland will offer first and second run sound.