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PRINTING MOTION PICTURE FILM 147
areas which were previously exposed, only the complementary section of each frame will be printed and the entire result will be as seen at 'P.
In practice it is not possible to rewind each scene and insert every matt as and when required and, when a number of transitions appear in a roll of film and, if the only available machine with which to make them is the Optical Step Printer, the more usual method is to prepare two complete travelling matts, each as long as the duplicate negative which is to be copied. The actual technique is more easily understood from Figure 63. The negative is divided into two lengths so that alternate scenes are contained in each roll, for example, scenes 1, 3, 5, 7, etc., are contained in roll 'A', and scenes 2, 4, 6, 8, etc., are contained in roll *B\ For convenience in the illustration the scene lengths have been greatly reduced, as also have the times taken to complete the transitions.
Travelling Matt 'C* is threaded in contact with either the negative 'A' or the positive film onto which the complete picture is to be printed. The machine is then set in motion and the entire roll of negative 'A' is printed without interruption. As the work proceeds scene '1' will be printed quite normally until frames *E\ 'P and 'G* are reached, the corresponding frames 'H', 'J* and 'K' in matt 4C will then mask off increasing sections of the picture until it is entirely covered. From this point the matt 'C remains opaque for a distant dependent upon the length of scene '2' in negative 'B\ and a corresponding length of spacing (equal in length to scene '2* minus the distance occupied by the transition at each end of this scene) is inserted between scenes '1' and '3' in negative *A\ This length of spacing is also equal in length to the opaque film between 'K' and 'L' in matt *C\ On reaching frame *L\ matt 'C, the first part of the first frame in scene *3\ negative 'A', will be exposed, and as the film progresses the matt 'L\ 'M* and *N' will gradually open until the complete picture area is exposed.
By now the resultant positive film will contain scene T, closing off to no exposure at the tail, a length of unexposed stock and then scene '3', opening up with the desired effect. By running the entire roll of negative 'A' and matt 'C it is obvious that the positive copy will then contain every other scene of the final picture opening and closing with the required effects, but separated by distances of unexposed film. The positive film is then rewound and matt 'D' is accurately located either with the positive or with the negative 'B\ which now replaces negative 'A' in the printer. Since the leading edge of the positive film already carries scene