“We all get dressed for Bill,” says Vogue editor-in-chief Anna Wintour, paying the ultimate compliment to legendary fashion photographer Bill Cunningham, whose work has been featured in the New York Times Style section for 33 years. But who is Cunningham, the octogenarian-about-town whose days and nights are still spent navigating New York’s streets on a bike – his 29th; the other 28 were stolen – searching for the perfect shot?

First, it’s important to understand who he’s not: Cunningham, as captured in the new documentary Bill Cunningham New York, opening Friday, is not one to inject himself into the story. He praises the work of “professional photographers” but insists he’s not one of them. He adores the camera until it’s turned on him. He claims never to have dined properly in all his life, and says the thought of romantic attachment never crossed his mind. He was, by his admission, too busy admiring women’s hats.

Indeed, Cunningham, at 80, is a man defined as much as consumed by work, and he wouldn’t have it any other way. He does not want for a life partner, and he’s not interested in money beyond the bare minimum needed to live. He refuses gifts, for fear of losing his objectivity – “Objectivity over what?” he muses – and shrinks from the accolades heaped on him by his peers.

His style is neither conventional – he shoots his subjects on the fly, conveying the naturalism of an unscripted moment – nor intrusive. He is aghast at paparazzi who mob celebrities in the streets, hunting them down like hyenas in pursuit of wayward gazelles. “To torment people and chase them, that I couldn’t do,” observes Cunningham, who, having never owned a TV, rarely recognizes stars and shoots them only when they’re wearing interesting outfits. (He dismisses onetime subject Marilyn Monroe as lacking in style.)

Yet Cunningham, however opinionated, doesn’t like to play critic. He watches, he observes, he captures beauty for posterity and personal gratification. The idea of best- and worst-dressed lists is repugnant to him. As one model notes, he has never taken a hurtful photograph, and not for lack of opportunity.

One thing his subjects and colleagues agree on is that Cunningham is a difficult man to know – not because he’s unfriendly, but because he takes his pictures then rides away, on to the scene of the next shoot. The pictures suggest the warmth Cunningham so generously exudes on camera, as well as his boundless fascination with people and the clothes they wear. But there is something oddly impersonal about a man who keeps his cherished subjects at arm’s length.

“I have no idea if he's lonely,” wonders a Metropolitan Museum of Art trustee. It’s an understandable concern. Watching Bill Cunningham, we come to suspect that he’s not. A man driven by a lifelong obsession, he is as unimpressed by material comforts as he is dispassionate about meaningful companionship. Filmmaker Richard Press captures his eccentricities simply and without passing judgment, and the documentary’s appeal largely rests on that of its reluctant star, which is considerable.

By the end, we are left with as many questions about Cunningham as there are answers. That we bother to ask them at all is a tribute to the film’s effectiveness; we are as fascinated by this endearingly enthusiastic enigma as Press is. If Bill Cunningham New York lacks any startling insights into its subject’s single-minded world, it’s only to be expected. He is, after all, a hard man to know.

Bill Cunningham New York opens Friday at the Embarcadero Center Cinema and the Shattuck Cinemas in Berkeley. For tickets and showtimes, click here.