Back in the day: Mina Block with her son Doug in the late '50s (Photos: Truly Indie)

I have to be honest: When Doug Block first approached me about his new documentary 51 Birch Street (now playing at Cinema Village) -- a beautifully cultivated glimpse into the knowability and unknowability of one's parents -- I all but winced.

After all, here was a guy who pieced together decades of footage and photographs and diaries plucked from his folks' suburban Long Island residence, narrating his own quest to understand what they revealed about the nature of Mike and Mina Block's 50-plus-year relationship. His interviews unfold like Errol Morris shooting a wedding, with a succession of trenchant analyses by siblings and psychologists and rabbis speaking directly into Block's handheld camera eye. It was the most striving personal project -- with the biggest potential for self-indulgent disaster -- I'd heard of since Tarnation, and as cool as I wanted it to be, the reality was that I didn't know these people and couldn't be sure I wanted to.

But therein lies the beauty of 51 Birch Street: Neither could its own director.

"It was more like, 'How long could I resist making it before I realized it was inevitable?' " Block recently told The Reeler. He had been mulling a film about his daughter and what it meant to be a parent; he had already acquired hours of tape from interviews with his own mother and father. But when Mina Block (pictured above with her son in 1959) died in 2002 and his father Mike kindled (or rekindled?) a new romance soon afterward, resulting in a move to Florida and the sale of the family home, Block suddenly had other considerations.

"When I went out to our house and walked into the home, and I saw all of our belongings from 54 years being packed away and dealt with or not dealt with, it hit me so hard emotionally," he said. "The realization that I hadn't lived in the house for, I guess, 35 years, but (that) it still felt like home to me more than any other place. I knew that there was something going here that was definitely a story. But it wasn't the one I'd been working on. I still don't remember if it was the second or third time I came back, but I was with my Dad in the car and I asked whether he missed Mom. And he said, 'No.' That's when I thought, 'This has nothing to do with the previous film; this is a film on its own, and it's time to get going on it.' "

As portrayed in the film, Block's process comprised a formidable pair of investigations. Along with candid illuminations from his sisters, the filmmaker's interviews achieve an especially harrowing intimacy with a father with whom he admits never having been very close. Their warming to each other after Mina's death is barely noticeable amid the choreography of averted eyes and long slumps into silence; Block attributes his father's stoicism in large part to his World War II service, but he can't help noticing the 83-year-old's relative ebullience following a reunion and courtship with Kitty, his former secretary. As a son, the dichotomy virtually paralyzes him; as a filmmaker, his curiosity propels him headlong into myth, motivations and secrets.

"We really said a lot of things that we wanted to say," Block said. "It helped me to have the camera. I could ask questions that I never really would have had the guts to ask without it. I feel somehow that my father was more comfortable in an interview situation, too. He's very honest, and he's always been good if I ask him a direct question. I've just never been that comfortable asking direct questions, and he doesn’t ask me direct questions. But if I've put one to him, he would answer. Once you get into that mindframe, it's not so difficult."

Doug Block and his father Mike in 2005

He probes similar dynamics on his mother's side, electing after extended deliberation to read three boxes of journals accumulated over more than half of her marriage. Block illustrates their most potent revelations -- psychosis, loneliness and the unsettling comforts of sexual obsession -- in tightly edited, graphical asides that get at the soaring immediacy and insurmountable cost of her confessions. As she discovers, being in touch with herself -- a stifled 1960s suburban housewife and mother -- means sacrificing most of what supplies individual joy. But in Block's contemporary footage, her smiles are only semi-numb; they punch through the pixel grain with the knowing upturn of one who has had it both ways.

Block made his own sacrifices as well, acknowledging his ambivalence about wanting to know his parents better. "If you do, it means you're no longer a kid," he said. "You can't be a kid around them if you show them you're an adult." The discussions with his father, always punctuated with nervous digressions ("You need a binder?" Mike asks his son in one of many token offerings from the packing stages of his move), settle into straight dope on their last night on Birch Street: Was Mike Block faithful? Again, the son asks the question, the filmmaker gets the answer. You never quite forget he's either, and in an increasingly dodgy era of personal documentaries, you actually wind up feeling grateful he could be both (and speaking for myself, at least, to have your initial apprehensions proven wrong).

"I tried as much as possible to take myself out of it -- to not be on camera that much, to not talk about my feelings, to not make it about me or the impact on me," Block said. "I don't think that anybody wants to see someone's therapy on film. You really have to watch the tone and make sure that you're not trying to make yourself look good. Or even look bad. I felt like I was in it as a guide in this journey into family on which I wanted people to come along with me, and if it was too much about me or making judgments about me, then they wouldn't want to come. But if I could somehow just get them past that and they could project themselves into my situation, then they'd come along for it."