Exit, pursued by a camera: Backstage portraits offer a unique glimpse of stars relaxing at the Old Vic

Aformer stage hand at London's Old Vic theatre, Matt Humphrey, took advantage of his position backstage and asked the actors if he could photograph them in their dressing rooms and behind the scenes. His atmospheric shots of life backstage include a ghoulish-looking Rebecca Hall, as Hermione in The Winter's Tale, standing in the theatre's corridor, while Jessica Hynes holds her leg in a yoga pose in her dressing room before a performance of The Norman Conquests.

The Old Vic's artistic director, Kevin Spacey, looks unrecognisable as he gets ready to perform as the old lawyer Henry Drummond in Inherit the Wind. He even photographed Tom Stoppard backstage when he popped into the Old Vic regularly to oversee the production of his play The Real Thing.

Humphrey, who joined the stage crew as a fly man, who raises and lowers suspended scenery during a performance, at the Old Vic in 2007, is now the official photographer for the Old Vic Tunnels, under Waterloo Station. "It was an ideal opportunity to catch the hidden moments backstage. The challenge for me is finding the beauty in the process of making theatre," says Humphrey. "There is no way you would catch these sorts of natural shots if you were not working there."

Humphrey also plucked up the courage to ask Jeff Goldblum to be photographed in his dressing room in 2008, when he starred in Speed-the-Plow with Spacey. "All the dressing rooms are quite different," says Humphrey. "They were redecorated when Spacey took over – but they have since deteriorated. All the actors put up cards and photos of family. Ethan Hawke put up a Bob Dylan poster. It all depends on whether they are sharing or have a room to themselves."

David Suchet, wearing a dressing gown, is holding up an envelope in his dressing room, right before a performance of Complicit. Lesley Manville is sitting on a bed, beneath a portrait of Lilian Baylis, a former manager at the Old Vic, while reading the script for Six Degrees of Separation.

Sinéad Cusack sits in front of her mirror lights getting ready to go on stage for a production of The Cherry Orchard, directed by Sam Mendes. The married couple Niamh Cusack and and Finbar Lynch in Dancing at Lughnasa kept the door of their conjugal dressing rooms open. An unguarded shot of Michelle Dockery as Eliza Doolittle in Pygmalion shows the actress putting on her make up, while looking in a dirty and dusty mirror in the quick-change area. Paul Ritter is brushing his teeth after a performance of The Norman Conquests.

Hawke gets some fresh air at the stage door of the theatre during a performance of The Winter's Tale, dressed as Autolycus in a top hat and little glasses. Richard Easton is doing the crossword in his dressing room, complete with antique rug, during a performance of The Bridge Project. Andrea Corr and Simone Kirby do some yoga on the floor of their dressing room just before curtain-up on Dancing at Lughnasa. Morven Christie sits at the window during her time in The Bridge Project.

Juliet Rylance looks over the back of the chair in the star dressing room during The Bridge Project; Nicholas Hoult is sitting down in the doorway of the the roof of the Old Vic, while taking a break from filming X-Men; and Richard Eyre, who is about to direct A Flea in her Ear, is sitting in the front-of-house bar.

"All the actors were happy to have their photos taken in the dressing rooms, because I had forged a relationship with them as they passed me backstage every night," says Humphrey.

He even photographed Spacey again earlier this year in the upstairs rehearsal room at the top of the theatre for his 31thirtyone project, in which he has taken 31 portraits of actors in 31 days for charity.

"I convinced Spacey to have his portrait taken after playing table tennis with him. He had come to watch the the final of a table-tennis game between the cast and crew of The Real Thing. I wanted to snap him in this upstairs rehearsal studio where the former Old Vic photographer Angus McBean had taken many photographs. I managed to get a set of old theatre seats that were stripped out of the auditorium last year and positioned them where the light from the skylight falls beautifully. Spacey loved those old seats because they are a piece of the Old Vic's history."

Now Humphrey has turned to photography full time. He is relishing the role of official photographer for the Old Vic Tunnels, a multi- arts performance space. "It is about catching these moments off stage that are natural; these are the moments that the actors, directors and writers remember."

31thirtyone, Strand Gallery, London WC2 (www. 31thirtyone.com; www.matthumphreyimages.com) 1 to 7 November. Proceeds from the auction and exhibition go to the charity Crohn's and Colitis UK