International projectionist (Oct 1931-Sept 1933)

16 INTERNATIONAL PROJECTIONIST March 1932 vibrationless operation of the apparatus Makes it particularly suitable for soundfilm reproduction; in fact, these features practically predestine this machine as the sound projector of the future, as of course, the sound film tape requires an entirely even run through the apparatus, and an absolute synchronism is attained through the even conveyance of the picture as well as of the sound film. A further advantage, of special importance for sound film reproduction, is the noiseless operation of the driving mechanism. Scraping of the film, more or less present in all Maltese cross machines, cannot occur in this new apparatus. The careful handling of the film through the constant conveyance and its excellent guiding are advantages by which the sound film profits, since in the sound film considerable sound interruptions may be caused through the slightest damage to the film tape. The sound-ray apparatus developed for this machine combines with the projector, as seen in the illustration, to an entirety. It is directly set onto it, and is driven by a gear fitted to the main spindle of the projector — thus variations in speed cannot develop between the projector and the sound reproducing appliance. For theater use the machine is to be preferred not only for its particular adaptability to sound film reproduction, but also because of its good protection against danger of fire. A self-acting shutter worked by a mercury pump automatically cuts off the projecting apparatus and the film guide from the arc lamp as isoon as a speed below the admissible one has been reached. The film drums are located horizon tally, thus ensuring most careful manipulation of the film, of which reels containing to 4,000 feet can be employed. Special long leads to' the , drums cause burning film being drawn into the drum to be extinguished. The source of illumination is a mirrorarc lamp with automatic carbon adjustment, contained in a double-walled lamp casing lined with asbestos. Slide Projection For the projection slide plates, etc., the light of the arc lamp is thrown upward by a folding mirror, contained in the lamp casing, on to a second mirror. From this the ray is projected through the diapositive and through a special objective in the usual way. Thus with the aid of the folding mirror in the casing, changing-over from film or sound-film reproduction to dia-projection is possible without any adjustnient of the machine. To obtain stepless speed regulation of the film picture, a friction gear is fitted between the motor and the mirror mechanism— this permits a minute speed regulation and allows the speed adjusted when starting to be kept constant without the necessity of any readjustment. The usual method of regulation by means of a resistance starter may enable an accurate degree of adjustment 'to be attained, but not a constant speed, as the ordinary resistance will vary in proportion as it becomes heated. The stopping device' often provided in Maltese cross machines is not required in this apparatus, as the optical compensation in itself already periliits a speed reduction down to about two changes of pictures per second'. ' " Comparative Worth of D. C, Power Sources (Addenda) I REFERRING to the article in your February issue by Samuel Bagno, regarding comparative worth of D.C. power sources, we have a few comments to make in connection with our experience along these lines. We have found that small compact motor generators of the single unit, twobearing type prove very satisfactory for furnishing power -to the exciting lamps and to the field circuits of the loudspeakers.' A 4,000 mfd. electrolytic condenser connected across the generator terminals provides sufficient voltage for the most •exacting conditions when the power is jjteing furnished to the exciting lamp. No filter at all is necessary in connection v/ith the field circuits of the loudspeakers. M. G. Economy We believe that motor generators of proper design are more economical for exciting lamp and horn field supply than any other source of power available, when all of the costs, including maintenance costs, are takfen ihto consideration. The motor generator may be furnished with wool-packed sleeve bearings of. liberal design, which require very infrequent lubrication. A few drops of oil every two or three months is all that is required. Bearings of this type require practically no more attention than ball bearings, and are quieter running. As far as the brushes and commutators are concerned, if brushes of proper composition and design are used, there will be practically no wear of the commutator and only infrequent changing of brushes. The maintenance expense involved in connection with bearings, commutators, and brushes is practically negligible. The motor generator is furnished with very close voltage regulation, so that one or two exciting lamps may be operated Esco two-bearing motor-generator set, with panel from it with very little change in voltage. This condition is not obtainable in other forms of power supply. Motor generators may also be furnished with suitable filters for supplying power to all of the tube filaments, in addition to the exciting lamps and field circuits of the loudspeakers. It is important to provide sufficient filters for each of the circuits, and to be Careful that all the leads, etc., are shielded with metal. By this arrangement, the filtering is adequate to prevent objectionable noise in the loud speakers, and the voltage is maintained constant, whether one or two exciting lamps and photo-cell amplifier filaments are being operated at once. It is probably advisable to use dry batteries for the photo-electric cell itself, but all of the other low voltage powter supply often obtained from storage batteries may be obtained from motor generators with less maintenance expense, more reliability, and much less frequent replacements. William H. Haines, Electric Specialty Co., Stamford, Conn. 3,124 Advance Orders for New Cameron Book "Questions' and Answers," the new book by James R. Cameron and which is published by the Cameron Publishing Co., Woodmont, Conn., is proving to be the most popular projectionist book ever marketed by this company, according to an announcement of pre-publication orders received to date. More than 3,124 orders have been received for "Questions and Answers" prior to publication, and there is every indication that the 5,000 mark will be reached before publication of the volume on April 1. Advance sales on this latest book is another indication of the leadership of Cameron books in the projection field. A large majority of projectionists buy Cameron books upon announcement and sight-unseen, so well established is the Cameron trade mark of quality. Inquiries on "Questions and Answers," as well as on all other Cameron books, may be addressed to Cameron Publishing Co., Woodmont, Conn.