Portraits in Motion (Summerhall, Edinburgh)

A chubby young kid, about ten or so, stares down the camera lens in black and white. He's shaven-headed and cynical, trying to make himself look tougher and older than he really is. Suddenly, he springs into life; his eyebrows move, he fixes his glare, and then his face cracks. That scowl gives way to confusion, then laughter, then a big goofy smile.

Volker Gerling is a flick book photographer. He travels Europe, living off his art, and takes people's portraits en route. Portraits in Motion is a staged exhibition of his work. He holds these tiny booklets up to a video camera and whirs through the images therein. On the wall behind him, a short stop-motion film plays out.

We pose for photographs. We freeze our features into an expression of choice, be it a fixed smile or a faraway gaze. Gerling tries to get beyond that: to push past those poses and catch personalities. He holds up his camera to the audience and, instead of a single click, it whirs into action, click-click-clicking for ages and ages. He takes 36 pictures over 12 seconds. If you pose for a photo, you don't expect that.

Gerling's flick books capture those moments of surprise, that instant when masks melt away and fronts collapse. In catching people off-guard, Gerling gets something truthful. A woman on a train collapses into giggles and pushes the camera away. A middle-aged man looks up and grows irritable. A young woman struggles to suppress a smile. These are beautiful short films: strange snapshots of life, flush-full of character. His portraits of places, taken over longer time periods, aren't nearly so interesting. They're too familiar: DIY timelapse photography.

With people, you see the precise split-second when self-conscious gives way to honest reaction. Families react differently to couples, men to women, young folk to old. You can see all sorts in these shots: love, pride, humility, pain.

Twelve seconds is a long time too; long enough to grow awkward or to regain your composure and react. Two teenagers start snogging mischievously. A woman at a bar smiles, then whips off her top. Two boys with fishing rods remain stock-still, without even blinking, as the grass moves around them.

Each year, the Fringe throws up curios like this: little gems that let you see the world a little differently. Just delightful.

Portraits in Motion is at Summerhall until 30 August (not 17, 24)