Power and Passion: The Technology of Orgasm opens Friday at the Roxie in San Francisco, for its theatrical premiere. This light-hearted and informative documentary traces the evolution of one of the most significant pieces of hardware in contemporary life, the vibrator. It also provides a clear example of how sexuality is political and politicized.

In the 19th and early-20th century, physicians treated female "hysteria" — restlessness, insomnia, anxiety, uppitiness — by stimulating female patients to "a paroxysm of relief." The electromechanical vibrator was developed as a labor-saving device for doctors, allowing them to bring a female patient off in 10 minutes rather than an hour. As vibrators had became associated with porn, the film claims, they disappeared from magazine ads and medical offices circa 1930, reappearing to public view in the 1960s as "sex toys."

Moving interviews document how vibrators changed women's lives, alleviating their ignorance of their own bodies and allowing sexual independence and satisfaction. It is astonishing to watch evangelist of self-love Betty Dodson recount that until she was 35, she thought she was "genitally deformed," simply because her labia minora were longer than the majora.

Women's sexuality is still the object of legal and patriarchal repression, as demonstrated in a major focus of the film, the infamous case of JoAnne Webb. A Texas distributor for "Passion Parties" (think Tupperware, but with sex toys), the Chamber of Commerce member was arrested on obscenity charges: a Texas statute forbids possession of more than five vibrators. There are, however, no Texan restrictions on Viagra. (On Feb. 12, the Fifth US Circuit Court of Appeals struck down the Texas statute as a violation of Fourteenth Amendment rights to "private intimate conduct.")

Filmmakers Emiko Emori and Wendy Slick encountered some indirect repression themselves after they optioned the book on which the film is based. "We thought this would be an easy sell, actually," Slick recalls somewhat ruefully. "I mean, after Sex in the City!"

Emori's two Oscars for Best Documentary Cinematography were no help. "People are ready for a lurid discussion about sex or an academic one, but we fall in the middle." With the exception of a small grant from the Robeson Foundation, the directors funded the film themselves, by mortgaging their homes.

Passion & Power eschews explicit images, opting instead for tongue-in-cheek humor and what photographer Alfred Stieglitz termed "equivalences." Time-lapse photos of unfurling blossoms may be a familiar metaphor for the vulva, as are lightning bolts for orgasm, but the lacy, trailing jellyfish are a surprise and a delight. "We wanted to show it mainstream, to show it in classes, in women's studies," as they have, at schools including NYU, Cornell, UCLA.

The film is overly faithful to the book, The Technology of Orgasm: "Hysteria," the Vibrator, and Women's Sexual Satisfaction, by Rachel P. Maines, in completely excluding lesbians from this segment of history. "The definition of 'real sex' [i.e., hetero penetration] has been laid on all of us," Emori responds when questioned about this omission, "and it doesn't fit almost anyone, whether we're straight or gay."

As to why there is no mention that mid-century and later the vibrator carried a stigma of queerness, mere possession supposedly signaling lesbianism, Emori acknowledges the concept, then explains, "and that's why we were so tickled to see this company [Passion Parties], all these straight women, Middle America, so engaged with female sexuality."

Troubling as the absence of lesbians is, Passion & Power is nevertheless worthwhile, and can still be empowering for lesbians. One lesbian couple told Emori and Slick, "We went out and bought a vibrator after seeing this!"