Imelda Staunton - having a ball, Guys and Dolls at the Royal National Theatre, South Bank, 1982.

Waiting for her onstage call, Dianne Cutlack inhaled the greasepaint and took in the roar of the crowd at the Theatre Museum.

The backstage dressing room, an area of the theatre strictly off-limits to the audience, has always aroused fascination and curiosity. What goes on behind the scenes before the curtain rises? What goes through the actor’s mind as he or she prepares for a role?

From now until May 1 2005, the Theatre Museum, Covent Garden, seeks to satisfy that curiosity with The Dressing Room: Photographs of Actors by Simon Annand.

This collection includes portraits of some of the most celebrated actors to appear on the British stage, from Judi Dench to Michael Gambon, Cate Blanchett to Jude Law.

The majority of the striking black and white photographs were taken during The Half, the final half hour before the start of a play when actors prepare themselves, mentally and physically, for the performance ahead.

Stephen Fry. Annand says: "I was late, with only two minutes to go before curtain up, but he still made time for a photograph." Common Pursuit at the Phoenix Theatre, Charing Cross, 1987.

In Annand’s own words: "Whatever theatre actors do during the day, in the evening they have to go on the stage as somebody else. Sometimes it is a welcome release. Sometimes it is unbearable. The dressing room is the space where this psychological negotiation between the actor and a fictional character takes place."

Simon Annand has photographed this transformation for over 20 years. Formerly the resident photographer at the Old Vic under Jonathan Miller from 1987 to 1989, he has worked for numerous theatre companies, including Sadler’s Wells, the Royal Shakespeare Company, Comedie Française and the Moscow Arts Theatre.

His photographs record actors at the height of their careers (Frank Finlay as Captain Bligh, 1985; Eric Porter preparing for King Lear, 1987), as well as others whose careers have only just begun (Ben Wishaw as Hamlet, 2004).

To lend authenticity, the exhibit takes place in the Theatre Museum’s own dressing rooms. Recordings of backstage tannoy announcements and the actors’ warm-up routines add to the atmosphere.

Alison Steadman. "If she wanted to lie down flat she brought in a blow up lilo and used the corridor." Entertaining Mr Sloane at the Arts Theatre, Covent Garden, 2000.

The visitor is invited to wander the corridors and to examine dressing rooms strewn with ghostly relics of the actors themselves: make-up cases, empty wine glasses, crumpled tissues, vases of flowers and the ubiquitous good luck cards.

A portrait of Alison Steadman, in particularly cramped quarters at The Arts Theatre, makes the visitor realise that the average dressing room of London’s West End is anything but glamorous. Particularly in the older theatres, even headlining performers make do with facilities unchanged in size or appearance since Victorian times.

Part of the fun of an exhibition of this kind is spotting actors at early stages of their careers.

A very young-looking Colin Firth appears at the Old Vic (1985), Rowan Atkinson is photographed pre-Mr Bean (1984), Kenneth Branagh is shown at the Lyric, Hammersmith (1987), before his career in films, and Anthony Hopkins appears at the Royal National Theatre (1986), pre-Hollywood.

The exhibition features reluctant sitters as well as the willing. Spike Milligan, who hated being photographed to the extent he would never look straight into a camera lens, is seen preparing for Babes in the Wood at the Chichester Festival Theatre.

Imogen Stubbs getting away from it all, Hamlet at the Old Vic, Waterloo, 2004.

There are striking images of Cate Blanchett, focused and withdrawn as she enters her character, Francesca Annis studying her face in a hand mirror, Jane Horrocks, half-in and half-out of character, and Michael Williams, preparing for a role at the Shaftesbury Theatre, with a framed photograph of his wife, Judi Dench, on his dressing table.

The exhibit also pays tribute to the transatlantic connection, which has long existed in West End theatre, with portraits of Glenn Close, Martin Sheen, Greta Scacchi, and Gillian Anderson.

Simon Annand’s photographs capture the defining moment when actors exchange the everyday for the magical illusion, and gain the power to hold an audience spellbound.

For those who love the theatre, The Dressing Room is essential viewing.

Dianne Cutlack is a freelance writer who can be contacted at jcutlack@compuserve.com