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A Printer fo^ Simtiltaneous Printing — De Pue 151
theory that a, sprocket wheel sboukl be made to tit or accommodate any negative, old or new, but found that, so far as the sprocket holes were concerned in fitting the teeth, it was more or less a snare and a delusion; for while making the wheels small enough to accommodate twelve or more teeth engaging at one time, it brought on troubles when employing a new or unshrunken film, as it then allowed movement to take place, not only at the very point of printing contact with the negative, but allowed the film to have a movement throughout its entire contact with the sprocket teeth. But by making the sprocket wheel larger in diameter and by making the teeth less thick at the base, there was very little, if any, movement taking place at the actual point of printing. This, then, is the theory on which we proceeded to construct a sprocket wheel which would accommodate not only a new film but one somewhat shrunken, as well.
Now, we have found that a speed of eighty or eighty-five feet per minute has been a very practical one for printing continuously by means of our automatic light resistance control. Eighty-five feet per minute is a speed not too great for the light change, over a wide range of variations, to take place without a disagreeable effect on the eye, and so far as we have been able to determine, the quality of the picture was not changed when printing at this speed, or a very much slower one. Sufficient light to bring up a picture in a certain time for developing is necessary in either case, and running slower and getting very much less light to make up for the difference appears to be unnecessary. Therefore, a high speed is very much to the advantage of the laboratory.
There has been considerable discussion and writing regarding the back lash or movement of the sound printing sprocket wheel past the very narrow opening necessary. Of course, it is a well known fact that when employing the alternating current for the light source as well as for the motor drive of a continuous printer, where the aperture is sufficiently narrow, there will be traveling lines or varying exposures on the film, brought about by the light filaments fluctuating in synchronous movement with the motor; but it is also well known that where the aperture is of a certain width, this defect is eliminated, and we have found that an opening of one-fourth of an inch in width is allowable in using the alternating current on the light as well as on the motor. We have built