Ralph Arlyck’s marvelous documentary “Following Sean” is a thoughtful portrayal of two families of secular, assimilated and intermarried Jews.

The film encompasses the links and gulfs between two generations and two coasts, and between the ’60s and today. That’s a lot to contemplate, but it’s typical for one of the leading practitioners of the personal essay style of documentary.

“I don’t know if it’s Jewish to question, but I’ve gone to some meetings and seders of groups [such as] New Jewish Agenda, and I was blown away by how much questioning there was,” the soft-spoken New York-based filmmaker says. “I’m interested in doing that. I’m not interested in laying out a thesis at the beginning and then driving towards one point.”

Arlyck’s approach is to allow the characters to form the film, without imposing his own preconceptions. “I’m very interested in ambiguity, and this is not the central thrust of most documentaries,” he says. “I’m more interested in what people think than in facts.”

The Brooklyn native was a graduate film student at San Francisco State University in the ’60s, and living smack in the middle of the Haight-Ashbury scene. He turned his camera on Sean, the 4-year-old boy who lived upstairs, and the resulting black-and-white short — in which Sean matter-of-factly talked about smoking pot — achieved international notoriety.

For many viewers, Sean epitomized the laissez-faire spirit, rampant irresponsibility and unbridled dreams of the hippie generation. Thirty years later, Arlyck set out with his camera to discover what became of Sean.

The provocative result, “Following Sean,” opens Friday, Jan. 13 in the Bay Area.

“One of the central things that I try to do in the film is make the distinction between actors — doers — and observers,” Arlyck explained in an interview when the film had its local premiere in the San Francisco International Film Festival. “My mother was deeply involved in all sorts of causes — zoning, League of Women Voters, she tried to ban hunting in Rockland County. That comes out of some nexus of Judaism and progressive radicalism.”

Sean’s Jewish grandmother, Hon Brown, was also an activist, and emerges as one of the most interesting people in the movie. She and her late husband, Arch, were involved in the local Communist Party; he was also a union organizer.

One of the unexpected pleasures of “Following Sean” is its understated reminder of the role that Jews played in San Francisco’s progressive history.

“One thing that strikes me is that Hon is the absolute center of that family. Is she Emma Goldman or Molly Goldberg? She’s both. She has that strong sense of social justice,” Arlyck explains, while noting that in the film she always seems to be in the kitchen.

“She said to Arch at some point, when he had to go underground, ‘I’m not doing this. You’ve got to shape up and be part of this family.’ With all her dedication to the cause, and the Abraham Lincoln Brigade and whatever else, she never lost that strong sense of family. To me, that’s Jewish.”

While Sean’s parents split up and his adolescence was somewhat chaotic, Arlyck was a model of stability. He moved back to New York after graduate school and married a French Catholic woman with whom he has two adult children. Arlyck has made several well-regarded documentaries, the best known of which is “Current Events,” and has taught film production at several colleges.

“Following Sean” is a tender inquiry not only into how Sean and his family turned out — Sean, incidentally, married a Russian Jew — but how Arlyck’s family turned out differently. So Arlyck is a participant in his film, not just a chronicler.

“What could be more characteristic of filmmaking than being a watcher, rather than a doer?” he muses. “That’s a longstanding debate in journalism: Do you record or do you help people? I felt that tension a lot in the ’60s.

“Obviously there were some Jews in the ’60s — Jerry Rubin — who thought that they needed to be actors. For most people, it was a combination. You’d be active from time to time, then you’d go back to your daily life.”

As in “Following Sean,” it’s clear that Arlyck is speaking about — and revealing — himself.

“That’s something that’s always troubled me,” he says. “I’ve always wondered about, worried about, the degree to which you ought to be participating, and recording, and just living your life.”

“Following Sean” opens Friday, Jan. 13 at the Lumiere in San Francisco, the Act in Berkeley and the Rafael Film Center in San Rafael. Ralph Arlyck will be in attendance at the S.F. screenings Friday night and at the Saturday afternoon shows in Berkeley.