WASHINGTON -- Nicholas Nixon has been working on ''The Brown Sisters" for 31 years. He's not done yet.
In 1975, Nixon began taking an annual photograph of his wife, Bebe, and her three sisters. The four women always pose in the same order: Heather, Mimi, Bebe, and Laurie. So far the resulting series, ''The Brown Sisters," consists of 31 pictures. At the outset the youngest, Mimi, was 15. This year the oldest, Bebe, is 55.
Nixon, a professor of photography at the Massachusetts College of Art, is enjoying a national moment with the series. Two complete sets of it sold at New York's fall photography auctions, and three of America's premier museums are exhibiting it simultaneously. ''Nicholas Nixon: The Brown Sisters" is on view at the National Gallery of Art here through Feb. 20, and at the George Eastman House in Rochester, N.Y., until Feb. 5. It is also part of the Museum of Modern Art's current permanent collection installation.
Despite all this recent attention, ''The Brown Sisters" is not a great photographic achievement. It is a simple idea repeated into prominence. Virtually none of the individual photographs qualifies as an exceptional or revealing portrait. A couple are poorly composed, clunky.
Nor is it particularly original. Many of Nixon's contemporaries, including Sally Mann and Emmet Gowin, have focused on family portraiture.
The closest the series comes to the avant-garde is in its relation to seriality, the repetition of simple forms explored mostly by the minimalists, but also by photographer William Garnett, conceptual artist Dan Graham, and others. But artists had been exploring seriality for at least 10 or 20 years before Nixon started ''The Brown Sisters." Nixon's series started too late to be considered a part of that vanguard.
''The Brown Sisters" may not provide an intellectual thrill, but if it doesn't hit you in the heart, you're dead. In about 25 feet of wall space, we see a generation grow from youth into adulthood. Sometimes the sisters stand apart, sometimes they hold onto one another. Occasionally they smile; more often they look impassively into the camera. In the most tender photograph, two Browns are distracted by Mimi's apparent pregnancy: Heather reaches out to touch Mimi's stomach while Laurie smiles at them.
It's an appealing, romantic vision of family. We want to be Browns. We want to share their divine sisterhood. We want to feel what the 32d year of friendship is like.
The way museums hang the series makes it all the easier to enjoy its impact. Both MoMA and the NGA hang it in a grid 10 photographs long and three high, with 2005's picture alone to the right. A viewer can see the entire 31-year arc with the turn of a head.
In the upper left corner, the Browns are young and beautiful. The sisters are well lighted, and the intensity of their gaze into the camera is direct. Heather's squint, in 1978, might even be lusty.
As young people so often do, the sisters assert their individualism within the group. In 1979 Laurie and Bebe are standing next to each other, their bodies touching. But their heads are tilted in opposite directions, and Laurie's arms are crossed, defiant.
By the most recent photographs, the vehemence of youth has given way to the resigned shoulder slouch of middle age. Now the sisters are often backlighted, which hides the years that have accumulated on their faces. The lazy comforts of midlife show themselves in other ways as well: In 2003 and 2004, Laurie wears the same shirt. The selfhood of the 1970s is gone, too, replaced by a celebration of the group. In almost all of the photographs since 1995, the sisters are embracing or sharing warm touches. We've made it, and we've made it together, the newer photos say.
Or at least we think so. In actuality, all we know about the Browns is what we see contained in a few dozen black-and-white rectangles. Americans are accustomed to seeing photographs about people we don't know and assigning a narrative to them. Tabloid pseudo-journalism of the Us Weekly sort is based on the imagination of the reader: Here are a couple of grainy photographs of Brad and Angelina. You figure out what's going on between them. (Wink wink.) ''The Brown Sisters" presents a version of the same fantasy.
As with those photographs of Brad with Angelina's kids on the beach, we want to believe that the tenderness we see in the Browns' portraits is the real deal, that we're being let into a special moment with the dream family. In this series it does not matter what any of the Brown sisters does for a living, whether they're parents, if they're gay or straight, if one survived cancer or is divorced. Among family these things don't matter, right? We buy into that, too. Our yearning to be touched by humanity exceeds our need to be artistically wowed.
I also wonder if men and women respond differently to the series. Over the course of a couple of trips to MoMA and to the NGA, I've looked at people looking at the Browns. They walk back and forth, comparing and contrasting photographs. Men tend to settle around the early years, checking out the chicks. While they look over to the later years, they quickly return to the young women, as if they're afraid of how the opposite sex ages.
Women look at the series in the opposite way. They gather at the right-hand side, around the photos that seem more about longstanding intimacy than the beauty of youth. They are more willing to discuss the pictures with their friends. Men stare with their mouths open.
Viewers who spend only a few moments with the series or who get caught up in the compare-and-contrast game miss the most touching part of the work. Yes, ''The Brown Sisters" is about the family. But it's just as much about one Brown sister: Nixon's wife, Bebe. She's the third woman in every photograph, the blonde. Throughout 31 years and 31 photographs, only Bebe Nixon looks right at the camera every time, right at Nick, right at us. Yes, the series is about the Browns, but it's also about the relationship between husband and wife.