Motion Picture Herald (Apr-Jun 1931)

62 MOTION PICTURE HERALD April 4 , 1931 OP SCLND CEPC€DLCTI€N The BLUEBOOK School THE question was: (A) Describe the slit optical system and tell us exactly what the condition must be at each point oF element along the system if the best results are to be had. (B) Name the requisites for perfect results, insofar as has to do with the excitinglamp and its optical system. First of all, I want to give some of you chaps a bit of a jacketing up. Each week there are anywhere from 50 to 200 replies come in too late to receive consideration. If men away out in British Columbia are able to get their answers in on time, certainly the rest of you ought to be able to do it without much trouble. Pep up and get a trifle more busy. The following have presented acceptable answers to this question. Earl Boyer, Lester Borst, C. Rau and S. Evans, Leslie Yates, Thomas Peters, George Thompson, W. B. True, G. E. Doe^ John Kotarch, John Williams, Carl Daugherty, John Doe, Tom Turk, J. C. Hamlin, R. B. Whitnah, R. P. Franklin, Claud Addington, Andy Richards, Frank Mitchel, james McGuire, G. T. Baldy, Thomas Van Vaulkenburg, Harry Crowley, S. Kleine, Frank S. Cimms, Robert Dodson, Frank T. Jenkins, G. Stapleton, A. R. Reisman, D. L. Herbert, D. Marsh, Wm. Gibson, George L. Walker, D. L. MacArthur; Lewis Henderson and T. L. Woods. AAA And now, gentlemen, I am faced with a queer proposition. To this question many have returned excellent answers, particularly Earl Boyer, Lester Borst, John Williams, Robert Dodson, Leslie Yates and G. Stapleton. However, again there is not one of them which, from the publication viewpoint, shows up as well as does the reply of C. Rau and S. Evans, Victoria, B. C. The trouble lies here. I have recently published several of the answers of these two gentlemen, and since naturally each man likes to see his answer published, publishing too many of the answers of one person (in this case really two, but combined into one answer) may discourage others from sending in answers. Well, gentlemen, that is unfortunate, but I cannot do otherwise than select for publication the answer which seems, everything considered, best. That does not mean, however, that the answers of the men named in the list are not just as correct, as far as they go. Most of them don't go so far as do Rau and Evans, however, or else do not work it into such excellent form. Answer to Question No. 71 By F. H. RICHARDSON So all I can say is, won"t you work just a bit harder to make your answers a bit more complete, and to put them into the very best possible form ? Rau and Evans answer follows : "(A) — The nanie 'slit optical system' is applies to the condensing and objective lenses which are mounted in the brass barrel containing the mechanical slit. "The condenser consists of two plano-convex lenses (five-eighths of an inch in diameter in Western Electric and one inch in diameter in RCA installations), which are mounted apex to apex, so as to collect the light from the exciting lamp and converge the rays on the mechanical slit. "The slit is an aperture (in Western Electric, \y2 thousandths high by 3/16 inch wide; in RCA, .006 of an inch high by .51 of an inch wide), placed in a horizontal position in the barrel, through which the light from the condenser passes in the form of a thin line. "This beam of light falls upon an objective lens, which further reduces the size of the. beam (the intensity of this beam, however, is increased), so that when it reaches the film the beam is .001 of an inch high by .08 of an inch wide (in books put out by RCA, the corporation claims that the dimensions of the beam after it passes through the reduction lens should not be more than .(X)075 of an inch high by exactly .07 of an inch wide). "To get the best results from the 'slit optica! system' (granting that the exciting lamp, film and photo-electric cells are in good condition and adjustrnent) the condenser surfaces must be clean and polished ; the slit must be clean and in an absolutely horizontal position as regards the lines on the sound track of variable density on the film. That is, supposing a line to be running down the exact center of the sound track, the slit will be at right angles to this line. The surfaces of the lenses of the objective or reducing lens must be kept clean and polished. The projectionist is concerned only with the outer surfaces of the objective lens, as he is forbidden to disturb the seal made by the engineers on the assembly. The light from the objective lens must be focused sharply at the sound track of the film. In the case of Western Electric and RCA installations this is done by the service engineer, but the projectionist must know how to do it in case he is called upon to take charge of other installations which are not serviced. "One method of focusing the light from the objective lens on the film is to thread a piece of high frequency (about 8,000 cycles) film from the lower sprocket in the projector head to the constant speed or takeup sprocket in the sound head, closing the sound gate leaving the usual loop above it. Next, place a white card or paper to cover the opening to the photoelectric cell housing. Then, with the exciting lamp turned on, with the finger slowly pull the film down past the sound gate aperture, meanwhile watching the image of the sound track which is r^eproduced on the card. The lines of the sound track are greatly magnified on the white card. Should the lines be moving either up or down, as the film is pulled down, the image of the slit is not properly focused on the film. When properly focused, the lines seem to dissolve into one another at the center. When focusing, the entire assembly in the barrel is moved backwards or forwards until the correct position is reached, at which position it is clamped in place by a set-screw. AAA "(B) — Perfect results as regards the exciting lamp and its optical system may be obtained by having the lamp in good condition and adjusted correctly so that a maximum of its light will fall on the slit. A lamp that shows signs of blackening on its interior surface should be discarded, as this blackening will mean a loss of light. The filament of the lamp should be absolutely straight, with no signs of sagging. If the filament shows si?ns of sagging it means that the slit will not be entirely covered with an even illumination; therefore the volume and quality of the reproduced sound will suffer. The lamp must be adjusted so that its most intense light will fall upon the entire area of the slit. "In RCA equipments, this is done by placing a card at the opening to the photoelectric cell housing, turning on the exciting larnp, and adjusting the lamp, either up or down, until a clear white field in the form of a spot is shown on the card. This vertical adjustment is the only one necessary in RCA as the other adjustments are taken care of by the way the exciting lamp sockets are mounted. The RCA exciting lamps are usually three in number, mounted on a turret, so that the spares may be quickly brought into action by merely turning the turret. However, in the latest small RCA types, only one lamp, mounted in a bracket similar to the Western Electric form, is used, BLUEBOOK SCHOOL QUESTION NO. 77 — Are horns directional? What is the limit of sound distribution of horns? Explain, in your own way, just what might be the effects of wrong horn positioning in a wide auditorium. Should the theatre manager or projectionist believe the horn positioning might be improved, what is the proper procedure if the theatre be sound serviced? If it be not so serviced?