A man who works in fashion with the genuinely humble demeanor of Bill Cunningham is a rare find. But it’s equally uncommon to find a film about fashion that’s not trying so hard to be, well, fashionable. Unlike the swankiness of The September Issue, in which American Vogue’s editor-in-chief Anna Wintour affirms rumours of her being a tough cookie, Bill Cunningham New York examines a more altruistic soul.

Cunningham is an institution in fashion photography. Since Word War II he has been roaming New York, chronicling the dress codes of generations and spotting trends the moment they emerge. The son of a working class family, Cunningham made hats and delivered sandwiches before starting as a writer for The Chicago Tribune. He found the medium which enabled him to communicate his unique view of fashion after being given his first camera by photographer David Montgomery. Cunningham joined The New York Times in the 1970s, covering the city's nocturnal eccentrics - primarily a flamboyant crowd of philanthropists and models attending charitable galas. With his unassuming temperament, he treated his high-end subjects with equal enthusiasm as his street photography, the latter a hobby pursued with zealous dedication.

Cunningham didn’t invent the candid street snapshot, but he completely shifted people’s understanding of what’s considered ‘in style’. It was no longer about the price tag or the labels, but rather the originality in which an ensemble and its components were matched together. Celebrities were only worth a snap if they were pulling out what he referred to as ‘a stunner’. He also drifted away from the formulaic and head-on catwalk view, choosing to shoot from the angle of guests sitting in the front row.

Now in his 80s, Cunningham continues to wander the streets of his adopted city on a worn-out bike, sporting a trademark blue jacket (the same one worn by Parisian garbage cleaners), adding to his self-deprecatory nature. It took director Richard Press and producer Philip Gefter eight years to convince this man, whose life is all about documenting others, to be filmed himself.

Bill Cunningham New York demystifies his character at a leisurely pace, in the intimate and unscripted style of a home video. Press employed a tiny crew using a handheld consumer camera to follow the photographer, from spotting his subjects to the New York Times office. We also meet Cunningham's neighbours: sartorially savvy elderly ladies who indluge the camera by modelling the mad hats he tailored back in the '50s. They and he are the last residents of Carnegie Hall Studios. One might expect opulence behind these doors, but Cunningham’s home is just a mattress and an infinite stack of photos and negatives, most of them unpublished.

Press also manages to capture a few intimate, face-to-face conversations: fleeting moments of openness that tentatively tackle issues such as sexuality and religion. Such themes are approached with trepidation, as if we have entered a desolate room that’s been locked for centuries. Cunningham never got around to romantic relationships, simply because "there was no time". However, halting pauses and a mischievous smile suggest that homosexuality may have aided his workaholic (and Catholic) path. "Fashion is the armour for surviving everyday life", he claims in his supporting statement.

The strongest scenes are those where he's on duty. You don’t have to be a fashionista to appreciate the man's love for his work, twinkling behind a pair of restless, sparkling eyes. What is more, it's his vivacious and uncomplicated attitude towards glamour and fame - he couldn’t care less – that makes him an absolute treasure to hang out with. In fact, you miss his onscreen presence when the documentary switches to stories from leading industry figure, the highlight being Wintour’s tribute: "We all dress for Bill".

Bill Cunningham New York seems less interested in decoding the enigmas and more enchanted by its subject’s light-hearted spirit; this pioneer of the aesthetic eye exudes a contagious joie de vivre. He is indeed a pillar of American cultural anthropology, as witnessed in its most candid manifestations. To borrow one of Bill's mantras: "He who seeks beauty will find it", and Press certainly looked for it in the right place.

Bill Cunningham New York opens in selected UK cinemas on Friday March 16. A full list of screenings can be found here.