A farmer looking through a window notices crops and drainage and the soil type of the land below him. An estate agent sees properties and road access. An electrician sees wires. But the photographer has her eyes half-shut, looking at the light: “You have to practise looking at light. It’s never constant. It’s all to do with the sun’s angle from the earth. It’s a question of waiting. While we’re sitting here, there are clouds coming over, it keeps changing.” She holds up a sheet of white paper, as if to lure something over. Light lands on it at once, as if the sun had already imagined our conversation.

“You have to make a decision. First you think, ‘Where’s my light?’ Then you think, ‘How can I use it?’ You have to control it, I suppose. You don’t take a photograph. You make a photograph. The point is that light has to be funnelled through an aperture of some sort. I try to get people away from thinking the camera is the thing. The light is the thing. The camera is just a means of catching it. That’s what photograph means. It means ‘drawing with light’ – from the Greek.”

Light, her collaborator, is a rude, prolific, hyperactive artist. Its pencils move at unthinkable speed, always shooting through apertures and reacting with chemicals to make marks on the earth. It draws the stroke of a tree upwards towards itself. It draws a flower from underground, first thickening the line of its stem, then complicating the leaf form, then brooding and doodling and finally turning the whole sketch inside out to find new colours. Not only film, but almost everything is light-sensitive. Ice is etched by it. Wood is whitened by it. Skin is stencilled with strap-lines. Mud is crinkled with cracks. Forests are tilted. Winds are lifted. The shapes of chairs are bleached into grass. Moons are shrunk and grown and the ground under trees is covered with pinhole images of moonlight. Glow worms are charged. Stellar clouds are eroded, experiments altered, shadows rotated. Relentlessly, while all this is going on, straight lines are being drawn off surfaces through millions of eyes, so that optic  nerves may be flash-lit and imaginations printed.

Light nurse

In this partnership, the photographer is the more modest one, working hard, like a nurse getting everything ready for the surgeon. She wears dark clothes, moving like a shadow behind her instrument. When she’s photographing people, she soothes them into the right position: “That’s the whole thing about faces. If they’re in the sun, squinting, you don’t kind of get their essence. People can defend themselves when they squint.

“When I’m doing portraits, I tend to take people into quite dark spaces because then their pupils are very open. It’s what you call bright shade, when the sun comes in obliquely, bouncing off the walls or the ground.” She keeps talking, to make time for the light and the shade and the face to make contact: ‘I’ve seen people take a photograph and a cloud comes by and I’m thinking well why didn’t she just wait a minute longer? That cloud would have come over and diffused the light. Could you move your head that way a bit?

“But with landscape it’s different. I prefer early morning: September or October in England, they’re just the softest, most beautiful days. Once I was trying to photograph the sea at Dartmouth, going backwards and forwards on the ferry waiting for the sun to come up over the water and there was this girl on her phone. As the sun rose she held up her phone and went blink, like that, then she carried on with the conversation. I suppose everyone’s a photographer now.”

Alice Oswald was talking to Kate Mount.