Projection engineering (Jan 1932-Mar 1933)

Page 18 PROJECTION ENGINEERING per minute, and the sound recorded upon a seperate 16 mm. film (as is the standard practice of 35 mm. film), which is running at 36 feet per minute. The picture is now optically reduced, frame for frame, to 16 mm. for sharpness, detail and reduction of grain, and the sound track contact-printed, as above. This method of optically reducing from a larger size film to a Smaller is not new and' is quite extensively used daily, from 65 to 35 mm. with marked improvements over contact-printing of 65 to 35 mm. Optically reduced pictures allow, due to this sharpness, detail and reduced grain, far greater screen enlargement, retaining a much clearer and better-defined picture, and meet all requirements. Any recording operator can with very little training become proficient in the handling of the recording apparatus, and can deliver consistently the highest quality of work. Any com mercial 16 mm. film laboratry can, without changing their equipment, solution or process, handle these film developments. Printing machines which optically reduce a picture from 35 mm. to 16 mm. and at the same operation print 16 mm. sound track, are now ready for delivery, to film laboratories. Synchronizing sound-track apparatus has also been developed to assist the laboratories. Projection apparatus to operate the sound film has been designed in several models, using standard makes of amplifying equipment and loudspeakers. It will be possible for users of this equipment to have their choice of styles and models which will best meet their requirements, with prices ranging up to four hundred dollars ($400.00) for the complete equipment, ready to operate by merely plugging into any light socket. Apparatus powerful enough to fill a AAA hall, seating 300 or 400 persons, with screen 7 inches x 9 inches, or even larger, giving a picture clear and distinct, with sufficient amplification to give a full, clear reproduction, powerful enough to properly fill an auditorium, has been perfected. Field of Operation It would be impossible to satisfy all fields wishing to adopt 16 mm. soundon-film at the start. It is expected that the following fields will be thoroughly covered : educational field ; industrial field ; amusement field ; home field. Studios and trucks will be equipped as soon as possible, so that 35 mm. pictures as well as new subjects may be made into 16 mm. pictures in quantities. The new system herein described has been placed on the market by the Jones Research Sound Products, Inc., 729 Seventh Avenue, New York. Answers to technical questions Nos. 26—32 HEREWITH are presented the answers to Questions Nos. 26 to 32, which appeared in the January issue of Projection Engineering: 26. This is a characteristic of alternating-current circuits, where the current tends to create a counter electromotive force. Self-induction varies greatly with conditions, depending upon the arrangement of the circuit, the medium surrounding the circuit, the devices or apparatus supplied or connected into the circuit. For example, if a coil having a resistance of 100 ohms is included in the circuit, a current of one ampere can be passed through the coil with an electric pressure of 100 volts, if direct current is used; while it might require a potential of several hundred volts to pass a current of one ampere if alternating current is used, depending upon the number of turns in the coil and whether it is wound on iron or some non-magnetic substance. 27. A little leeway must be allowed in the answering of this question. Several factors must be taken into consideration, but let us assume that the glass surfaces of condensers and lenses are perfectly clean and that the maximum of light is being picked up by the condensers from the arc lamp. Take the crater of the arc as 100 per cent, only approximately 33 per cent of this is picked up by the condensers on d-c, while on a-c. the percentage is a great deal less. There is a reflection loss amounting to 4 per cent at each of the four glass-to-air surfaces of condensers, plus an absorption loss which can be reckoned as 6 per cent per inch, assuming the condenser combination to have an axial thickness of \y2 inches, then the total loss by absorption will amount to 9 per cent, or a total loss of 25 per cent passing through the condenser combination. Thus only about 25.75 per cent of the light from the arc reaches the film being projected, the light loss due to film density will of course vary greatly, but it is safe to assume that the loss amounts to 50 per cent, which leaves us with only 12.85 per cent of the original 100 per cent. In its passage through the objective lens this is reduced some 25 per cent — 4 per cent reflection loss at each of the 6 glass-toair surfaces ; therefore only 9.65 per cent emerges from the objective lens. This is again cut 50 per cent by the flicker shutter, leaving only 4.80 per cent of the original 100 per cent. Other factors cut this percentage down, distance to screen, effective aperture of objective, etc. 28. Mazda motion picture lamps are designed for operation base down within 25 degrees of the vertical, at any greater angle performance will be impaired. They are made for use at constant current rather than constant voltage. The lamps must be operated at their rated current — for instance, at 31 amperes the life of the 30 ampere lamp will be reduced about one-half. 29. A prismatic condenser cannot be used when showing slides because the risers of the prisms deflect the light so much that dark rings appear in the beam near the condenser where the slide would have to be placed to be cov ered by the light beam, although they are filled in by the crossing of the rays further out in the beam. 30. Exciter lamp currents not correct, storage battery discharged, exciter lamp out of focus, photocell defective, sound gate aperture clogged. 31. Pickup defective, one power amplifier defective, voltage amplifier defective, storage battery discharged. 32. The input and voltage amplifier panel is made as a single unit and is similar to the two panels used in type A equipment. Duplicate controls on the panel are provided for two projectors. They consist of two exciter lamp rheostats, with meter jacks, two projector control switches, with pilot lamps to denote which projector is connected to the amplifier, a single test meter with extension cord and jacks for reading plate current and bias voltage. In the type B equipment the voltage amplifier has the gain control following the second stage. Tubes used are first and third stages UX-210 and the second stage UX-841. As previously announced many of the sets of answers to this series of questions are not worded the same as the answers that are published each month. This does not mean that the answers ■ sent in are not substantially correct. The purpose of the questions is to give projectionists an opportunity to test their knowledge by attempting in their own language to answer the questions presented monthly and then, later, check their answers against the set of answers published.