17.5 Mm
Standard 17.5 mm magnetic film uses 35 mm magnetic film which has been slit lengthwise into two equal widths and lengths before use. The "heads" of one-half of the 35 mm donor become the "heads" of one 17.5 mm length while the "tails" of one-half of the 35 mm donor become the "heads" of the other 17.5 mm length. 17.5 mm magnetic film was often used as a secondary "shop standard," perhaps most notably at Paramount and Universal, for location dialogue recording and it was most often run at 45 feet/minute, one-half of the usual 35 mm magnetic film speed, thereby achieving a 4-to-1 increase in economy although at a significant sacrifice in sound fidelity, but certainly adequate for monophonic dialogue. For stereophonic dialogue, conventional 35 mm magnetic film was used.
For final mixing, the 17.5 mm dialog was usually initially copied to a 35 mm center track or full coat magnetic film element, whereby the dialog track entered the conventional mixing process as a second-generation 35 mm duplicate.
17.5 mm film, in this context, is for magnetic sound elements only, and only for very cost-conscious producers.
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