Opus (Matt Helmet, 1970)

Opus is nine minutes of avant-porn in which a heterosexual couple have sex with Toshi Ichyanagi's "Extended Voices (for Voices with Moog Synthesizer and Buchla Associates Electronic Modular System)" on the soundtrack (although it seems to be spliced in with another piece). A curio at best, it still ends conventionally with a money shot. According to the Erotica Films blog, the performers are Natalie Nell and John Joseph and the festival mentioned in the opening credits is The Second Wet Dream Film Festival (1971). 

Grade: B-minus