Joan Marcus knows her way around a theater.

She has spent a quarter-century shooting professional productions in Washington and New York, where she has emerged over the past decade as Broadway's preeminent production photographer. Lately, she has helped define the public image of some of the Great White Way's latest hits ("Wicked" and "A Raisin in the Sun," for example) -- and misses ("Taboo" and "Never Gonna Dance").

Her job is to take the photographs at the beginning of a show's life that accompany reviews and other media coverage.

But she was backstage at the Kennedy Center last week for a much different, more private photo shoot. During a performance of "The Glass Menagerie" in the Eisenhower Theater, just days before the production closed, Marcus was taking portraits of the actors -- in costume and in character.

The portraits aren't for public consumption. They're for Marcus's personal collection of black-and-white portraits. She has taken the pictures with casts of nearly a dozen other Eisenhower Theater productions dating to the '80s.

Marcus does the portraits only at the Kennedy Center, where she started as a photographer's assistant in the '70s after graduating from George Washington University. She honed her skills there as a production photographer -- first as a freelancer, later as a staffer -- in the '80s and early '90s, before moving to New York.

At first, Marcus recalls, she pursued the idea of character portraits as a way to enhance her studio lighting abilities. Since production photography depends on choices the lighting designer makes to illuminate the stage, setting up her own lights in the Eisenhower's greenroom -- its backstage lounge area -- gave Marcus the freedom to experiment with ways to light and photograph subjects she was familiar with.

The effort, however, quickly became more than a mere technical exercise.

"I normally shoot in the dark," Marcus says. "This is different than what I do on a daily basis. There's more interaction -- you get to know people. As time goes by, it becomes a record of your life."

Actors are asked to participate on a voluntary basis, and Marcus gives them free rein in presenting their characters to the camera.

"Everyone approaches performing differently," she says. "I don't try to control them too tightly."

"The Glass Menagerie" and "Cat on a Hot Tin Roof," another Kennedy Center production mounted this summer, mark Marcus's return to backstage portraits for the first time since 1997, the end of the center's heyday for original productions and out-of-town tryouts for Broadway-bound shows -- the kinds of productions that Marcus found ideal for her portrait work.

Though she was often hired for production photography at the center even after relocating to New York in 1992, it wasn't until she was brought in to work on the center's recent original production efforts, 2002's Sondheim Celebration and this summer's Tennessee Williams Explored festival, that she was inspired to revisit her backstage portraits.

"I would like to do this in New York," she says, "but I can't."

The theater environment there, she says, is too high-pressure to allow for the kind of informal, organic photographic sessions she enjoys at the Kennedy Center. Washington, she says, is a "kind place."

Though professional actors might seem unlikely to perform tasks outside their contractual obligations, especially during a performance, Marcus says no one has turned down the invitation to pose. The cast of "The Glass Menagerie" was no exception.

Most were chatty when Marcus wasn't shooting, discussing other productions, sharing news about common acquaintances. Star Sally Field, on the other hand, squeezing in her portraits before the curtain went up for the night's performance, intently whispered key lines to evoke her character -- the iconic Amanda Wingfield -- for the camera.

"I love the idea," says actor Jason Butler Harner, the production's Tom, adding that he has long admired Marcus's artistry. "You can tell that she senses when a moment is coming on stage, and you can linger in the moment longer because you know she's capturing it."

Jennifer Dundas, who played Laura, says the character portraits added another level of appreciation to her role.

"I think of these characters as real people in Tennessee Williams's life," she says. "It feels right to have a record of the people as we've portrayed them. I can imagine the characters sitting for a portrait."

Tiki Davies, head of the Kennedy Center's press office, hopes Marcus's character portraits eventually can be exhibited at the center, though there are no such plans at the moment.

"I find them astounding," says Davies, who worked at the center in the '70s when Marcus was starting out as a photographer's assistant. "I love the fact that she works in black-and-white. There's a haunting quality to them. I look at them and they're so still and contained -- so different from production photos."

Marcus is more modest about what she has achieved with her portraits: "Not every single one is a gem."

Still, her pride in her work -- the production shots and her private collection -- is unmistakable.

"I've almost become a person of the theater," Marcus says, "more than a photographer."

Joan Marcus, above and below, jokes with Sally Field, who was appearing in "The Glass Menagerie," while photographing the actress for her collection of character portraits backstage at the Kennedy Center. A portrait of Roger Robinson from the 1985 Kennedy Center production of "The Iceman Cometh."