You pass the entrance to the “Diane Arbus Revelations” exhibition, which opens to the public at the Metropolitan Museum of Art next Tuesday, and enter an octagonal room with one picture on each of the six walls not a doorway. The first picture to the right is “Triplets in Their Bedroom, N.J. 1963,” a gelatin silver print on 20-by-16-inch paper, an image of three virtually identical girls, perhaps 13 years old, dressed alike, sitting on the middle of three identical beds. The girls are wearing long dark skirts and boys’ white, long-sleeved, button-down collar shirts buttoned at their wrists and necks, and white hair ribbons. The modest clothes suggest they are Orthodox Jews, and the patterned wallpaper, the quilted bed coverings, and the banal decoration on the headboards suggest a comfortable but pedestrian family environment. The girls’ faces are oval, their dark hair held neatly back by the ribbons, their features pleasant but unexceptional, their expressions intent upon the photographer. (The middle girl seems to be suppressing the hint of a smile.) It is a fascinating picture.

“Triplets in Their Bedroom” succeeds through restraint. The straight-ahead relation of the subjects to the camera might be something Arbus absorbed from the great German documentarian August Sander. The light is even, probably a diffused flash. The converging lines of the sides of the beds draw attention to the faces of the girls, as does the contrast between their pale faces and the complex geometrical pattern of the dark wallpaper. The tripletness is not sensationalized but presented as the basic fact of the image. The viewer’s eyes shuttle right to left, left to right, back and forth, peering into the girls’ faces to see how there can be three such girls so similar yet obviously each a unique soul. The picture demonstrates both Arbus’s respect for the people she photographed and for the formal properties of her chosen medium.

The other five pictures in the octagonal room include some of her best known images, for instance, “A Young Man in Curlers at Home on West 20th Street, N.Y.C.” (1966) and all are printed on the same 20-by-16-inch paper. This size is large enough to allow comfortable gallery viewing, without seeming to be pumped on steroids, as too many contemporary photographs do. The walls are a medium taupe: Somber in keeping with the subject matter, neutral to show off the rich black-and-white prints. Here and throughout, Jeff Rosenheim, the museum’s associate curator of photographs, has organized the exhibition so there is enough room for the individual print to always be the center of focus. The spare selection in the unusually shaped room is a stunning introduction to an impressive and moving show.

Nearly all of the 180 photographs on display are portraits. We know Arbus was familiar with Sander’s work and, like him, shot people of great wealth and little, of all ages and stations, of artists, of the physically deformed, of circus folk, and of the mentally retarded. But whereas Sander maintains the neutral pose of the social scientist throughout, Arbus at times exposes an attitude: For instance, there is something mildly derisive about “A Family on Their Lawn on Sunday in Westchester, N.Y.” (1968). True, the 40ish mother is an attractive blond, but she lies on the lounge with her eyes shut tightly, the father covers his eyes with his hand and seems to be smirking (at what?) and the young boy bent over the plastic wading pool in the back has his butt to us. The vast expanse of their suburban back yard is an arena for them to be alone together, hardly a family at all, and not having fun.

Both Sander and Arbus are masters of detail. “Mrs. T. Charlton Henry on the Couch of Her Chestnut Hill Home, Philadelphia, Pa. 1965” is loaded with information: Her intricately beaded dress, her four-stranded pearl necklace and matching earrings, ring, and bracelet, the other ring and bracelet, the patterned couch upholstery, the chinoiserie of the table lamp, and most especially her absurdly fluffed-up hairdo. In “Woman With a Briefcase and Pocketbook, N.Y.C.” (1962), the subject maintains her dignity even though the sidewalk she stands on is littered with pigeon excrement. In Sander detail is essential to his project of taxonomy; in Arbus detail establishes the geographical and social place of her subject, but the photographer is called to transcend it, to separate a core of being from the data.

It is important that, again as in Sander, most of Arbus’s subjects are looking at her. When they don’t, as in “A Family on Their Lawn” it means something. In 11 of the 12 negatives on the proof sheet from which she selected “A Jewish Giant at Home With His Parents in the Bronx, N.Y. 1970,” the three are grouped together and face the camera. In the selected frame, they are separate and look at one another, because the subject is not so much who they are, as who they are to each other. The complex expression on the mother’s face – tender, appalled, frightened, loving – is the center of the image. But in the typical Arbus photograph, it is the photographer and her subject who are looking at each other.

“A Young Man in Curlers” is a headshot. We see the long fingernails because the hand is held up, but we see the bad skin, the badly penciled eyebrows, the stray hair because the camera is so close, and of course we can not miss how unattractive, how not soigne, this person is. But if Arbus is looking at him, he is looking at her, and maybe at the points in the middle of his eyes where her flash is reflected as two tiny white dots, what he seems to be saying to her is, “I am lost.” A photographer needs talents beyond mechanical technique for her subjects to see in her someone to whom they can expose themselves that way.

Emmanuel Levinas, the great 20th-century Talmudist and philosopher of phenomenology, maintains that we see God in one another’s faces. Diane Arbus was not a religious person, but she had spiritual aspirations, and I expect that for someone with such a visual appetite, such a voracious eye, seeing and being seen was a form of devotion.

March 8 until May 30 (1000 Fifth ue, at 82nd St., 212-535-7710).