Home Movies and Home Talkies (Jun 1933-May 1934)

266 HOME MOVIES & HOME TALKIES A similar state of affaii-s can be jiroduced by over development, which again can be regarded simply as too much chemical action. While for picture work over exposure and over developnaent, if not carried to extremes, can be tolerated and indeed sometimes are pvu'posely sought for certain effects, they are quite out of the question for sound recording. It is clear, then, that both as regards exposure which meant the intensity of the light coming from the recorder lamp and development must be controlled within the safe limits of the sensitive film. The practical way of looking at this is to consider that the two duraktmin ribbons in the light valve bow outwards and inwards due to speech current fluctuation whereas normally they are straight and parallel. The intensity of light from the recorder lamp must be such that when the ribbons are bowed outwards to their maximum the film must not be over exposed nor under exposed when they are drawn inwards so as to almost touch. This is shown pictorially in Fig. 60. Recorder Lamp Adjustment Different brands of film stock and batches made at different periods are liable to vary a little as regards their sensitivity and thus have to be tested. A short length of film is given a series of exposures in a device known as a sensitometer, which is nothing more nor less than a gradually shaded mask. The strip is then developed with a standard sohition and for a definite time, after which it is examined with an instrument known as a densitometer, which is really a type of microscope after the style shown in Fig. 61. /R^//vr//yG D'^uM Fig. 62. Printing Sound Films 5our/0 77?fiCK P/?//vr//vo P/cra/?£ From this test strip of film it is possible to pick out the mean density which must be matched in the light valve recording machine when the ribbons are unmodulated. It is clear that from the test strip we know exactly the capabilities of the film we are handling and can therefore adjust the brightness of the recorder lamp to give us what we want. In practice recorder lamps are calibrated to their corresponding film densities. Put in another way, we may state that the current flowing through the filament of the recorder lamji is adjusted by means of a resistance to suit the sensitivity of the film stock being used. Development Details A common method of printing sound track and picture on one film is first to mask out the sound track, then print in the picture, repeating again with the picture mask while the sound track itself is printed. After this comes development and printing of the compared film. Unfortunately, however, experience shows that a f/c ro/?E //fASf< P'emo vbo P/?//VT/fVG T^fiCK Of? 'S/l.tir/7-S " sound track requires less development than a picture, which places us in a somewhat awkward predicament since both are on the same roll of celluloid and must pass through tlie same development baths. What is actually done is in the original development of the film bearing the sound track alone, which by careful control will give us the effect of under development after printing on the same film as the picture. The Printing Machine Before the advent of the talking picture there were two types of printing machine in vise known respecti\ely as the continuous and step hy step. In the former the negative and unexposed positive were passed together continuously before the light. In the step by step system, however, printing took place section by section in a similar manner to projection. In fact it was possible to make use of a projector for printing or, better still, press a camera into service. From quite a brief consideration it is clear that only the continuous process is .suitable for sound-on-film work, for one cannot take liberties with the soimd track, which unlike the ])icture is not broken into frames. Most ])rinting machines consist essentially of two large sprocket discs round which the film passes before <> printing light. In the Bell iV Howell printer arrangements have been made as shown in Fig. 62 for viuyiiig the aperture so as to allow for full width pictm-e as for silents oi' for ^ound track alone or for picture alone. From the point of view of the ainateui this may be a minor point, l)ui It indicates what a vast amount 111 detail change was necessitated by I lie imroduction of sound. This picture gives a good idea of the amount of light required in a modern studio production. Notice the banks of lamps in the foreground To the Editor oj Home Moviks ani> Home Talkies Di';aii Sik, — May I express my appreciation of your policy of publishing technical books at a jirice to suit the man in the street. " Film Technique " should imdoubtedly be in the possession of every serious amateur jjroducer and I am sure you will be doing the amateur movement a I'eal service in reprinting such works. — Yours faithfully, A. D. Frischmann. 27 Mincing Lane, London, E.C.3.