It was a simple idea: one family, photographed at the same time every year. Zed Nelson has traced Sue and Frank’s transition from new parents to grandparents. What’s it like to see your life pass in front of you?

In the summer of 1991, photographer Zed Nelson, then 25, invited a couple of new parents he was acquainted with to visit his London studio. Oh, and bring your baby, he said. At the time he had ambitions to be a travelling photojournalist. Within the year, he would fly out on the first of a series of visits to far-flung conflict zones. But for this, Nelson had in mind a quieter, more domestic project. He set up a backdrop and lights, and he encouraged the visiting parents – a personable couple called Sue and Frank whom he’d met at a party – to pose with their newborn, Eddie. The parents held hands, wild-eyed, visibly shot through with the terror and excitement of parenthood. Eddie, weeks old, oblivious, considered his own fingers and dribbled. It might have been any other family portrait.

Except that Nelson invited Sue, Frank and Eddie back to his studio for more portraits, at the same time of year, every year, for as long as they agreed to come. He would chart the evolution of a parenting life, with Sue fixed in position on the right of the picture, Frank on the left, Eddie inching up between his mum and dad. “Same backdrop every year, same lights, same camera, same angle,” Nelson explains, thinking back over the finicky logistics of a project that has run since 1991 without interruption. “Every year I measure out the distances to the inch. It drives us all a bit mad. But we do keep coming back.”