International projectionist (Jan 1943-Dec 1944)

DESIGN OF SUB-STANDARD SOUND PROJECTORS (Continued from page 9) by increasing the difficulty of maintaining the film in the focal plane of the sound scanning system. Of equal importance is the avoidance of wow and flutter. The adoption of designs which have proved successful in the 35-mm field for maintaining a constant film speed is, I am aware, beset by difficulties, notably the increased weight and cost, and the problem of avoiding patent infringement; nevertheless, development in this direction is a logical step. First, there must be complete isolation of the film in the sound head from the intermittent motion, by means of an interposed sprocket and a free loop; next, the method of stabilizing film speed in the sound head must be improved, preferably by the adoption of the fluid-flywheel or magnetic drive.8 A question sometimes asked is whether there is any advantage in making use of the projection lamp for sound excitation, as is done in some projectors, as compared with the use of a separate exciter lamp. One advantage certainly is that there is a large filament image, and condenser adjustments can. therefore, be dispensed with. A 100-cycle mains hum can sometimes be heard when running on a.c, but, due to the large thermal inertia of the filament, this is rarely noticeable. Economy is effected, both in the provision of an additional lamp and its holder, and in the power supply circuit. A serious defect is, however, that the projection lamp has to be of a nonstandard type, burning cap upwards; standards should certainly be fixed for lamps of this type. The points of design so far discussed are fundamental to any type of sub-standard projector. Let us turn to a rather different aspect. 16mm Versus 35-mm Increasingly in future the 16-mm film is going to be compared with 35-mm. A point that is often overlooked is that, while the projector upon which the substandard film is shown is generally a fairly light portable machine with all the objections that portability entails, the 35-mm film with which it is compared will be shown generally on a static type of machine where weight and size are virtually unlimited. Sub-standard projector design must develop along two distinct lines. There will be many static situations where the need is for a machine virtually a miniature of the normal kinema projector. I envisage a very considerable demand for machines of this type in news-theatres, in publichalls, and in the many village and church halls that will be built or re-built after the war. In the opposite direction is the portable projector. Here, lightness and compactness are important virtues. The machine must be easily assembled and quickly brought into operation. Let us consider the former type first, since, although we have yet to see such a machine, there is little to be said about it — simply that it must in most essentials follow the lines established for existing kinema projectors. It must employ an arc — or possibly later a discharge lamp — as illuminant. The gate must be efficiently cooled to withstand the intense concentration of heat in an area less than a quarter that of the 35-mm frame; the machine will not need to be enclosed and noise is unimportant. The whole machine must be substantially built, a pair of them' capable of running a 12-hour programme daily without undue depreciation either of machines or films. One thing I would urge is that the whole machine — projector, soundhead, and illuminant — must be regarded as an entity, and that we should not get led into the cardinal fault of 35-mm equipment, that is, the manufacture of the mute head, sound equipment, and arc by different firms, whose various products are used together indiscriminately and without regard to their respective suitability. The projector and soundhead must be a single unit, easily demountable from the stand. It would be of value if the soundhead were capable of connection to the existing amplifiers, otherwise it will in some cases necessitate the duplication of amplifiers and speakers. Here especially particular care is needed in the design of the picture gate, since such a machine will normally be used with short-focus wide-aperture lenses, in order to obtain the requisite picture size and brightness. Film buckle must at all costs be avoided. The points I made previously are still more vital — the avoidance of film buckle by means of a curved gate, and the reduction of gate heat by means either of air or water cooling. As I have already suggested, •036 ~ ~ PROJECTOR APERTURE •017* -024.5 '0155 FIGURE 3. 16-mm. film showing lands. the average projectionist will, in default of a non-intermittent projector, prefer an intermittent sprocket to a claw. Such will be the machine which I envisage will be demanded for installation in a large number of kinemas and other public auditoria. But this does not alter the fact that a large proportion of the market will be better served by a transportable machine. There is scope for a variety of types, from the purely amateur machine and the semi-professional type — for instance, for educational purposes — to the fully professional model. Recommendations Some admirable recommendations on the requirements of projectors for educational purposes are embodied in a leaflet issued by the British Film Institute6, many of the proposals would apply equally to other types of machine. The principal objects of the proposals are simplicity, and ease of control and maintenance. To quote a few points from, this leaflet: Controls should be planned so that, as far as possible, they are brought to a control panel on the right-hand side of the machine. Control knobs should be of distinctive shapes, so that they may be distinguished by touch. Furthermore, a standardized system of color-coding for controls should be introduced, so that controls on a strange machine are immediately recognized. Sequence interlocks should be provided to prevent operations being performed ire such an order as to damage either film or machine. ( This relates chiefly, of course, to the lamp and motor switching, which, should be controlled by the one turn-switch to prevent the light being shone on stationary film.) Plugs should be so designed that it is impossible to insert them in any but the correct socket. (/ would also add — in any but the correct polarity.) Every effort should be made to reduce mechanical noise to an absolute minimum. Fixed speed controls should be fitted enabling the machine to be run at fixed speeds of 16 and 24 frames per second. Threading should be made as simple as possible. . . . There should be an inching device, and if a screw is used for the purpose, it should give a visual indication of the position of the claw (if fitted) when threading. (A trip device should operate automatically if loops are lost — a device undoubtedly calculated to reduce film damage.} Still-picture device and reverse are required, the latter on silent machines and where possible on sound machines also. (Difficulty may arise in the latter case from the soundhead loops.) A power rewind is demanded. Independent levelling and tilting devices are urged. Finally — an important point — "Direction of rotation of feed and take-up spools should be standardized so that films are not wound inside-out." One may regret that greater stress was not laid upon the fundamental point of reduction of film damage. Another point to be mentioned is the elimination of SEPTEMBER 194 4 IS