Movie Makers (Jan-Dec 1953)

MOVIE MAKERS Leaders and trailers [Continued from page 234] for this forthright and clarifying discussion. Queried on the same matters in connection with the company's magazine-loaded films, Mr. Mentch reported further : "Our magazine-loaded films do not generally bring up questions of the type listed in your letter, because magazine film requires less leader and trailer. For your information, however, a 16mm. magazine film has 18 inches of leader and 18 inches of trailer. The length of the film returned to the customer by our processing laboratories may vary between 50 feet 2 inches and 50 feet 9 inches. An 8mm. magazine has 12 inches of leader and 7 inches of trailer. After slitting, about 50 feet 3 inches are returned to the customer." From these statements, and from the definitive tables supplied by Ansco and the Kodak company, the following facts emerge : (1) Both film manufacturers package, in each of their nominal footage units, film footage well in excess of the amount stated on the carton. (2) This excess footage, however, is supplied not for picture making but (A) to protect the nominal film footage from fogging, and (B) to provide expendable footage necessary to the companies' laboratory procedures. (3) No movie maker, when using properly the film loads of Ansco or the Eastman Kodak Company, need fear that his processed pictures will be returned short of the total film footage promised by the manufacturer. But how, you may well ask, can I be sure that I am using Ansco or Kodak film loads correctly? For the magazine film user there obviously is no problem, since it is impossible to expose these films in any manner other than that intended by the manufacturer. For the roll-film user, the footage indicator of practically every spool-loading camera makes provision for running the leader footage through before the actual footage indication begins. Likewise, zero (0) is indicated before the film actually runs off the feed spool. Furthermore, in using Eastman film, the cautious movie maker can be doubly sure that none of his opening scenes will be spoiled by the perforated emulsion number at the beginning of the reel. He simply threads his camera and sees that it is running properly before he closes the cover. After closing the camera, he removes the lens, thus revealing the threaded film in the camera gate. With his eye on this film, he now runs the camera until the perforated frames have passed the gate. He then stops the camera, puts back the lens and he is ready to shoot. In order to protect himself against losing part of a scene at the end of a roll, he watches the footage indicator carefully and, when it reaches zero (0), he places his hand over the lens and runs out the rest of the film. In other words, if you want to make sure that all of your scenes are complete as you filmed them, simply keep within the marked limits of the footage indicator on your camera. That's what it's there for: to protect you against alleged "robbery" at the processing laboratory. Projector speed control [Continued from page 239] As the speed falls, the action of the switch drops out of step with the rectifier action. If the speed falls enough, the other extreme is soon reached. Here the switch is closed for the whole time the rectifier is blocking current. When this happens, motor current flows through the rectifier for one half of the time and through the switch for the other half. With the greater current so provided, the projector speed therefore increases, heading for the 19 fps set by the speed control resistance, R. As soon as the speed begins to rise, however, the switch opens during part of the time the rectifier is blocking current. Motor current is therefore cut off during this part of the cycle and the rise in speed is reduced. In this way the system adjusts itself so that the rotary switch operates exactly 60 times a second. If you fix the switch on the projector flywheel, the projector speed is determined by the number of times the switch opens and closes with every turn. The flywheel revolves once per frame. So if the switch makes and breaks at every quarter turn, the projection speed is a quarter of 60, that is 15 frames per second. This is near enough to the usual 16 fps to be quite satisfactory. Fig. 2 shows the switch I fitted to my NORMAL CENTER FIG. 3: In this arrangement the film, on its way to projector's feed sprocket, passes over sprocket D, which drives switch thru gearing. 24a own projector flywheel. You will see that it has three sectors so that it makes and breaks a path between two carbon brushes (shown removed) three times for every turn. On the British 50 cycle current, this gives a projection speed of 16 2/3 frames per second (one third of 50). On the American 60 cycle supply, however, the projector would run at 20 fps. At this speed, films shot at 16 fps may appear rather hurried on the screen, so that I would definitely recommend four sectors instead of three. The details of construction depend to some extent on your projector and your resources. The essentials are a metal disc or ring carrying four insulating sectors. The surface must be trued up on a lathe so that two vacuum cleaner motor brushes can rub on it. In the interests of your safety, see that the ring and brushes are all insulated from the projector frame. The rectifier is a heavy current radio type. Your radio service man will provide the right type if you specify 150 milliamps. (or more) and 170 volts (or more) peak inverse voltage. These figures will suit a 115 volt 60 cycle supply. The switches can be any type intended for use on the power supply. Your radio man will supply these and also a 6 volt 0.3 ampere flash lamp to connect in series with the rotary switch. This lamp gives an indication of the current through the switch and also overcomes any tendency for the speed to run alternately fast and slow. The condenser should be connected straight across the switch brushes to prevent arcing, which would cause radio interference. Although 15 frames per second is perfectly satisfactory as a projection speed, you may prefer to run your machine at a true 16 fps or even at 24 fps. This is quite a simple matter if you drive the rotary switch through gearing. For example, you can put a 32-tooth gear on the switch and drive it from a 30-tooth gear on the flywheel. Then the switch will revolve 15 times a second when the projector is running at 16 frames. If you are going to use gearing, however, it is a good idea to keep everything as a separate unit in order to avoid drilling holes in your projector. Fig. 3 shows the sort of scheme I have in mind. Here the film itself turns the rotary switch as it passes round the sprocket D on its way to the normal feed sprocket. The sprocket D turns the rotary switch through gearing chosen to produce the exact speed required. By making the attachment fit on the spindle intended for the feed reel, you can make it applicable to any projector. Of course the attachment must in turn carry a new spindle on which to place the feed reel. Compared with mechanical couplings from projector to tape recorder, this simple gadget has the advantage of placing no restrictions on the positioning ©f the two machines. You can stand