This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.
When 16mm was first developed, 35mm silent films were shot for
projection in an aspect ratio (width to height ratio) of 1.33:1; thus,
the 16mm aspect ratio of 1.37:1 was designed to be relatively close to
the 35mm one. Unlike 35mm, however, no modification of aspect ratio
was needed in order to accommodate sound-on-film prints (the sound is
printed on one edge of the film, in the space formerly occupied by a
second set of sprocket holes [which are still present in todays
`double-perf' camera films]), and so the aspect ratio of 16mm remains
unchanged.
Unlike camera films, 16mm release prints are almost always single-
perforated-i.e. the film has perforations on only one side of the
image. The other side is reserved for a soundtrack. The only exception
to this are lab workprints from double-perf camera stock, which are
also printed on double-perf stock, mostly for convenience in splicing
with a `guillotine'-style tape splicer, commonly used by editors.
 
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