Having lost the match, a distraught young boxer storms through the changing room, swearing and punching at inanimate objects. Watching him explode, it’s impossible not to fear for the safety of the person behind the camera.

But that person is Kirsten Johnson, the remarkable cinematographer behind such fearless fare as Fahrenheit 9/11, Citizenfour, Darfur Now and This Film Is Not Yet Rated. She's faced much worse frontline scrapes in her time, and confidently tracks the young pugilist until the shot takes us somewhere that is as moving as it is surprising.

This Brooklyn-based sequence is one of many narrative threads in Cameraperson, a feature film composed mostly of outtakes from the award-winning cinematographer's previous work. Only a director of photography of Johnson's peerless calibre would open her "memoir" with an out-of-focus shot of dirt.

That’s typical of a film that continually questions the nature and purpose of its own medium; that so frequently privileges silence over discourse; that deconstructs every trick and trope.

For almost 40 minutes, Cameraperson unfolds as reportage, a travelogue that brings us to such far-flung locations as a maternity hospital in Nigeria, Yemen's Sana'a detention centre, Afghanistan, a Muslim family's farm in Bosnia, Darfur, a Texas courtroom, Guantánamo Bay and Manhattan's Ground Zero.

“These are the images that marked me,” says Johnson in an introductory title.

You’ll have to trust her: she’s going somewhere with this, and so are you.

These competing strands are patiently teased out into small, compelling dramas, with large ethical dilemmas attached. The film-maker includes footage of her mother, who had Alzheimer’s, and notes her passing. Johnson’s warmth ensures that the off-screen inclusion of this event, is, like the rest of the film, a kind of love letter to everyone she has lensed, be they family members, court officials, a frightened young woman in a health clinic, or Jacques Derrida.

Too often, collections of rarities and B-sides contain material that ought to have remained just that. But Cameraperson's scrapbook of outtakes and downtime surpasses any of Johnson's greatest hits.