We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
324 PRINCIPLES OF CINEMATOGRAPHY
was removed from tooth No. 1 and as perforation 'A' reached and disengaged from the peak of this tooth.
The obvious remedy for this condition is to shape the curved tooth surface to a curvature more acute than the true involute and, when this is done, the film will gradually slip backwards whilst the leading edge is riding up the tooth face during the stripping operation. This condition is seen in positions 3, 4 and 5. In 'position 3' the film has commenced to strip from tooth No. 1 and, since the curvature of this tooth is less than the true involute, the gap 'C between the next perforation and tooth No. 2 is now less than gap 'B' in position 2. In 'position 4' the film has nearly completed its passage in stripping from tooth No. 1 and, in consequence, the gap 'D' between the second perforation and tooth No. 2 is even less than gap 'C in 'position 3'. Finally, in 'position 5', the film is just about to disengage from tooth No. 1 and the gap between the second perforation and tooth No. 2 has now been eliminated and the drive has been transferred to this new point of contact.
It should now be apparent that, under these conditions, the film will have two speeds. Firstly the maximum speed, that is, the speed which exists when no stripping action is in progress and, secondly, the slipping speed or that speed which exists during the time the drive is being transferred from one tooth to the next. Obviously, the same conditions will apply when the film pitch is longer than that of the sprocket teeth or when the sprocket is operating as a hold-back between the sound head and the take-up spool as in a projector mechanism.
Three main conditions exist under which the film can move at different speeds. Firstly, when the gap between the second perforation and the second tooth is not completely closed by the time the film is completely stripped from the first or driving tooth. This condition will give rise to three film motions, (a) a maximum speed during those periods when no stripping is occuring, (b) a slower speed during the time of stripping and (c) a distinct jump backwards at the moment when contact with the leading tooth is lost and the drive is transferred to the second tooth. Secondly, when the gap between the second perforation and the second tooth is just closed at the moment when the film is completely stripped from the first tooth. This condition gives rise to two film speeds, (a) a maximum speed when no stripping is taking place and (b) a slower speed during the time of stripping. However, under these conditions, no jump back period will occur. Thirdly, it can be arranged that a perforation commences to strip from a sprocket