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.
This high relative humidity would be encountered only in extreme cases, but these cases are believed to exist often enough so that they should receive consideration. Under these conditions the film is wide enough so that trouble can be expected if the effects of moisture8 have not been taken into account.
Note that more than half of the films are oversized according to ASA specifications under conditions where 90% relative humidity prevails. It is not possible to guess what percentage of the films would cause jams, but it is possible to see that the spread of values for the 16-mm film made from 32-mm film is greater than for the 16-mm film made from 16-mm stock.
Shrinkage of Film
The longitudinal pitch of film found in exchanges, or its shrinkage, is generally a matter of more importance to the designer of projectors than to the current user or the original purchaser. The pitch is generally affected very little by the operations of the processing laboratory. It is true that some processing equipment, which uses high tensions, can stretch the film put through it by about 0.05%. This value is negligible compared to the changes in length that come with time.
Figure 10 shows the distribution of longitudinal shrinkage for all films measured in the exchanges. Note that there is no film with a shrinkage over 1.7%. To design sprockets for film of greater shrinkage than this will generally give sprocket teeth that are quite thin if there are many teeth in contact with the film. If a design value as small as 1.5% is adopted, then there is a chance of about one in sixty that the perforations in some film will interfere with the sprockets and be damaged. Actually, the choice of longitudinal dimensions is also affected somewhat by the local deformation around the edge of the perforation. This deformation is caused by tension put on the film by the sprockets, a
20
1.0 PER CENT
Fig. 10. Distribution of longitudinal shrinkage.
matter discussed by Vilbrandt9 several years ago.
By referring to Fig. 8, we ought to be able to obtain the narrowest (maximum) width of film measured in the survey. Actually 0.6215 in. was the lower range of the gauge, and so we could not read smaller values. There were lj% of film in the class 0.620 in. to 0.622 in. Accordingly, the uncertainty is not a great one, and indeed not a vital one. In general, if a 16-mm projector is designed for wider film than that used, little harm will be done to the film. There will be no tearing of perforations as is the case when the longitudinal pitch is below the design value, though soundtrack placement will be affected. Sound-track placement was not measured in this survey. It may be expected that the errors of placement would be about the same as those of centering the film in slitting and would .show a fluctuation about as great as the variation in width.
Thanks are due to those in the industry who made possible this survey and particularly to Daniel Botkin and Eldon Moyer of our division for their care in taking many measurements and reducing the data to useful form.
A. C. Robertson: Dimensions of 16-Mm
409