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152 Transactions of S.M.P.E., Vol. XIII, No. 37, 1929
this printer on the theory, however, that most laboratories are equipped with the direct current for their light sources, and therefore, have divided the machine into two parts so that the printing lamps can be used on the direct current; this is to allow the sound tract opening to be closed down to any width desired. Our tests show that we can employ the same lamp for the sound tract as in printing the picture, and therefore, can keep the construction of our automatic light change uniform for all printers for which they have so far been used. They take 100 watt lamps for continuous printing, and 250 watt lamps for step optical printing.
In making tests on the sound tract opening, we have not yet discovered any defect in printing at this rate of speed and with an opening of three-eighths of an inch. In fact, we think that with the direct current, and that size opening with a sufficiently strong illumination such as a 100 watt lamp, it is perfectly practical when driven by the means we have employed in that connection; that is, a worm drive of 16 2/3 to 1 and coupled directly to the motor by a universal joint. This means gives the driving sprocket wheel a very uniform and continuous speed of 103.6 revolutions per minute. Our drive for the picture negative is transmitted from this sound tract sprocket shaft directly to the sprocket wheel of the picture aperture. Any slight variation in the movement, if it should occur, would not be serious in this way of driving, while the reverse method might have more or less serious defects on the sound tract printing.
It has seemed advisable to build a machine which would handle a thousand foot reel of film with one automatic light set-up and as a continuous unbroken print for developing machines. Therefore, this machine running eighty feet per minute will print a one thousand foot reel in just twelve and one-half minutes, if running continuously. That is at the rate of forty-eight hundred feet per hour, if negatives of that length could be handled without a stop. By allowing for four thread-ups and rewinding of the negative (of course, the rewinding of the positive for printing is eliminated and that time is saved), it is safe to say that three thousand feet or possibly three thousand five hundred feet, with a more skilled operator, is to be expected from this speed of printing.
Up to this point I have not dwelt on the fact that this printer has been developed to print from two negatives, the sound tract negative being handled as a separate negative which, of course, will