At a time when every other photographer (including her own husband) wanted merely to photograph housewives or pin-ups, Diane Arbus offered abrasive, intimate portraits of society’s strange. From drag queens, circus freaks, religious zealots, struggling middle-class families, and the mentally handicapped, she found lives no one else bothered to consider, and Arbus portrayed them with frank humanity and empathetic warmth. She unearthed and inspected hidden worlds, yet allowed all her subjects’ inner monologues to stay well-kept.

But as Arbus once famously quipped, “A photograph is a secret about a secret. The more it tells you, the less you know.”

The enigmatic, reclusive Arbus had her own secrets, some of which the Walker Art Center’s recent exhibit of her work, titled “Revelations,” tried to divulge. The showing offered many personal artifacts including journal entries, family photographs and letters to friends in addition to Arbus’ actual work.

However, the real biographical truth was in the scores of portraits lining the Walker’s walls, not in the voyeuristic exposé of the items of her past. Who Arbus was as a person was most evident through the faces of others.

This is one of the many reasons why “Secretary” director Steven Shainberg’s “Fur: An Imaginary Portrait of Diane Arbus” is so troubling. If you’re expecting to learn about Arbus, perhaps more than the exhibit offered, you certainly won’t find it here.

“Fur” makes it immediately clear that it is not a historical biography. Instead, Shainberg wanted more of a “tribute” of sorts, choosing to invent characters and situations outside of reality as if to explicate the mysterious three-month period in 1958 before Arbus abruptly stopped assisting her husband in their family studio and took a leap of faith into her own artistry.

But here is what “Fur” decides to keep secret: Arbus’ Jewish upbringing, the poet brother who overshadowed her frowned-upon work, her marriage at a young age, her eventual separation, the real names and lives of her two children (one of whom also photographed), the art instructors she studied under and what ultimately lead to her suicide at the age of 48, days before releasing a widely anticipated portfolio of limited-edition prints.

Instead, Shainberg envisions Arbus as a trapped housewife (Nicole Kidman) who unhappily assists her husband (Ty Burrell) in photographing other, more typical women. Arbus is anything but typical, drifting through her domestic life painfully shy, bored with the ordinary, and frightened by the odd desires and dark obsessions she keeps buried inside.

All that changes when a man named Lionel Sweeney (Robert Downey Jr.) moves into the apartment above her family. A wigmaker and former circus sideshow attraction plagued with a condition that covers his body in thick, Wookie-like hair, Lionel seduces Arbus away from her confines into bizarre, fairy tale underworlds (glum morgues, glittering drag clubs, sitting in on a dominatrix prostitute slow dancing with a naked client) that eventually inspire her rebellion.

Addressing the inner passions Arbus likely wrestled with, especially in a society that kept its desires locked safely behind closed doors, is one of “Fur’s” few engaging aspects. Yet, while the film clumsily attempts to follow Arbus’ mental unbuttoning and insatiable hunger to create, her camera remains unused and any actual portraits untaken. Shainberg could not get the rights to any of Arbus’ images, so “Fur” ends up coming off as too timid to approach the terrifying power of her work.

The performances are, for the most part, great – that’s not the problem. Kidman is at her usual icy-beautiful. The real surprise is Downey, who patiently sculpts one of the film’s most difficult characters as a perfect romantic lead: sexy, sincere and heartbreakingly sensitive, even when buried under all that fur.

But, though Kidman and Downey have convincing sexual chemistry, their parable plays out all too typically. Yes, their love story is actually meant as a metaphor for artistic urge. Still, did Arbus have to fall for a circus freak in order to become a photographer of the freakish? And did it have to be a man that inspired her?

“Fur” would have done much better without the “Diane Arbus” tag on its title. The film is erotic, tragic and beautifully made, maintaining an uncompromising dedication to an artist’s creative coming-of-age. But as a biography – oops – “portrait,” it is an unflattering one and far too out of focus for a figure as deserving as Arbus.