Irving Klaw, Riding the Human Pony Girl.
Source: the Internet Archive.
Published under a Creative Commons Attribution 3.0 Unported (CC BY 3.0) licence.
1950s. One of the earliest examples of pony play fetishism on film. Includes fancy bondage, some light spanking, and girl-on-girl pony riding. Half way in the two mistresses have to stop and change the slave’s arm position. One wonders if this was intentional or a mistake in planning. Note the elaborate leather harness, wrist restraints, and face mask.
Unlike the crude, amateurish fetish films of the 60s, which are either over-exposed or too dark, Klaw’s movies have proper lighting, staging, and relatively smooth camera work and editing.