"Theoretically there's no such thing as a colour photograph," Jessica Eaton tells me authoritatively as she guides me around her debut British exhibition, Ad Infinitum – though her brightly coloured geometric photographs dramatically refute this statement. Her images are, in fact, complex illusions made by the inner workings of her analog camera.  Eaton uses light the way painters mix colours. Her images nod to colour field painting, Bridget Riley, Josef Albers and Sol LeWitt. And her end results are both formally beautiful and, the more you look at them, mesmerising in their tonal depth. This Canadian-born artist has created a considerable buzz of late – and now she has the backing of the Photographers' Gallery for this show at the Hospital Club, in London's Covent Garden.  Her complex works owe nothing at all to Photoshop, but emerge out of a painstaking process that melds technical expertise, chance – and a degree of surrender to hit-and-miss, old-school technology. "My fuck-up rate is pretty high," she says. "On average, one work out of every 200 sheets of film. I think of it as a kind of strategy game. There is a lot of waiting and concentration involved."  It's a way of working that takes some explaining – especially when you realise that the colours you see never exist in reality. The bright cubes come about because of a "tripartite additive colour process" she stumbled across in an ancient Kodak manual. Eaton makes actual cubes, which vary from 5 to 25 inches, paints them in various shades of grey, then shoots them over and over on the same negative. Each time, she places a red, green or blue colour separation filter over her lens and, with each exposure, the three colours eventually merge to become her signature vibrant, geometric cubes. (If you look closely, you can still see the rough textures of her painted surfaces, which gives them an unlikely arts-and-crafts earthiness.)  "I'm basically exploiting the interior of the camera," she says. "The colours mix inside it. With paint, mixing colours is a darkening process, but light works in the opposite way, making increasingly bright colours each time. If I kept going, I would end up with a pure, brilliant white."  For more complex cubes, Eaton flips over the back of her camera and shoots more than one cube on the same piece of film. And for her blurred, retinal-scorching squares, she even moves the camera up and down as she shoots.  Why squares and cubes, though? "I adhere to Sol LeWitt's idea that you find the most beautiful unobtrusive object that can be used over and over again until it disappears, and the idea becomes the subject."  Intense and intellectual, even when hungover and jet-lagged, as she is when we meet, 36-year-old Eaton is the hottest photographic artist to come out of Canada since Jeff Wall. To acknowledge this, the Canadian cultural attache opened her London exhibition with a speech that mixed deadpan humour and obvious pride in her achievements. Born in Regina, Saskatchewan, Eaton currently lives and works in Montreal, a city more renowned for its groundbreaking rock – Arcade Fire, God Speed You Black Emperor – than its art. Next year, she will relocate to New York and embark on her next exploration, of still lives of flowers.  Her work is a dramatically beautiful response to the ongoing debate about photography's meaning in our age of relentless digital distraction. But it will divide opinion. "I think photography is still relatively conservative in terms of its artistic possibilities," she says. "I suppose one of the big questions I am asking is: what is inherently photographic?"  That is as pertinent a question now as ever it was.
She creates eye-scorching squares that look like digital confections. But they're actually painstakingly handmade – and nothing you see here is really in colour