This documentary chronicles Bill Cunningham, a man obsessively interested in only one thing: his pictures that document the way people dress. The 80-year-old New York Times photographer has two columns in the paper's Style section, yet nobody knows who he is.

A quiet achiever.

Bill Cunningham defies any of the preconceptions one might have of a person whose job title is The New York Times’ chief fashion photographer. Modest to a fault, the indefatigable 80 year-old brings an anthropologist’s focus and bucketloads of enthusiasm to his task of spotting trends on the world’s runways, and analysing their mutual dependencies with the style of 'everyday New Yorkers’.

The shutterbug darts about New York City on a pushbike (his 28th, after the theft of the other 27), compiling images for his dual NYT columns, 'Evening Hours’ and 'On The Street’. The former brings him into frequent contact with the uber-A list of New York society, where they greet him like an old friend, but he seems at his happiest when spotting Manhattan’s random trendsetters, at whom he clicks with whippet-like reflexes before they disappear from his viewfinder.

Cunningham’s columns are a working cultural document of NY’s sense of style, and the montages are fascinating as much for what they say about the trajectory of a runway look to a high street, as they are an indicator of precisely how many women it takes to make a stonewash denim pencil dress a 'trend’.

A collective of well-groomed talking heads chronicle Cunningham’s career as a milliner-turned-fashion historian, and their insights speak volumes about the origins of this pillar of integrity’s faultless work ethic. Ramifications of an early run-in with a corporate overlord have clearly shaped his worldview; they are reflected in Cunningham’s eventual exit from Women’s Wear Daily on ethical grounds (after its editors changed his copy to mock images of 'real’ women wearing runway fashions), and his ongoing refusal to accept so much as a glass of water from a function organiser for fear that it might change the dynamic and thus, undermine his objectivity.

In file footage, he describes fashion as 'the armour to survive the reality of everyday life", and to be sure, the film’s glimpse at his personal life reveals it to be in sharp relief to the flamboyance of the rag trade. Cunningham leads a monastic existence in what little time he doesn’t spend behind the lens each day: he sleeps on a makeshift stretcher bed amongst the filing cabinets of his tiny studio atop Carnegie Hall (he’s one of the lone holdouts fighting developers intent on turning the hallowed art spaces into call centre cubicles); the confirmed bachelor also hints at a deep spiritual connection with a Higher Power that trumps any feelings of regret he might have otherwise felt for the lack of a romantic partner.

Reportedly, it took some eight years of coaxing before director Richard Press wore Cunningham down and he consented to being profiled. And why not? The reclusive octogenarian has spent the greater portion of his waking hours observing others. From anyone else in the fashion industry, such demurrals about the limelight would have more than a whiff of false modesty. In Cunningham’s case, however, he’d simply rather deflect the spotlight onto a beautifully constructed garment, worn well. (An insider at Paris fashion week plucks Cunningham from the anonymity of a queue, admonishing the gatekeeper for overlooking 'the most important person in the world". Cunningham appears grateful but you get the impression he’d have been happy to wait it out and spare everyone the fuss.)

'I’m not interested in celebrities and their free dresses," he tells the gathered throng (to scattered applause) when he accepts the Legion of Honour for his services to Fashion. Later, he backs it up as he turns his attention away from Catherine Deneuve, because 'she wasn’t wearing something interesting".

In the tradition of the best observational documentary (including that created by his subject), Press crafts a story about artistic passion that questions the value placed on cultural preservation by a thriving metropolis, and taken further, why we ought to be shocked that a successful man with unrelenting integrity, humility and a tireless work ethic should be thought such a remarkable oddity.