Journal of the Society of Motion Picture Engineers (1930-1949)

July, 1943] FILM DISTORTIONS 91 produce in-and-out of focus troubles from other causes, we sometimes find that film that has been embossed has also shown in-and-out of focus troubles. Flute or Long Edges. — The fourth type of film distortion, flute or long edges, is now seen more often with safety film than with nitrate film. A typical example of flute or long edge film is shown in Fig. 2. It is caused by shrinking the center of the film without shrinking the edges or, conversely, by stretching the edges. (a) Flute from shrinkage of the center of the film: When film, especially safety film, is projected repeatedly at high heat intensities, the center tends to shrink more than the edges, causing a particular type of flute often known as "twist," since a strip of film stretched between two points gives the appearance of being twisted. FIG. 2. Flute, or long edge, in cine film. (b) Flute from stretching the edges of the film by means of recessed rolls: The edges of the film are often stretched in processing machines by pulling the film too tightly over recessed rolls while the film is wet or while it is hot. (c) Flute from stretching the edges of the film by the use of twisted strands: Occasionally processing machines are designed in which the film is turned between each pair of rollers so that the emulsion side will never be in contact with the rollers. If the distance between the rollers is too short this twist puts an additional strain upon the edges of the film which often produces flutes. (d) Flute from stretching the edges of the film through swelling of the edges: Flute is sometime produced in raw film if a tightly wound roll is exposed to very high humidities. Moisture is absorbed by the