The first picture one encounters upon entering the National Gallery's new photography exhibition, "Irving Penn: Platinum Prints," is a 1948 view of a photographer's studio in Peru.

Titled "Cuzco Photographer With Woman Wearing Shoes," it shows a rural Indian of Incan descent sitting for her portrait. Behind her is a painted backdrop of an idealized scene dominated by a colonial hacienda. In front of her stands a tripod-mounted camera and, bent over it in silhouette, the photographer whose studio this is.

As unlikely as it seems, this anonymous Cuzco studio photographer might well be the alter ego of Irving Penn, who spent the bulk of his illustrious career working in New York for the fashion magazine Vogue.

The Cuzco photographer unpretentiously earns his living from his craft. He finds unexpected beauty in unlikely subjects while modestly allowing his subjects to present themselves directly to the camera. He collapses the distinctions between "naive" and "sophisticated" cultures, complicating our responses to his work. He does this, paradoxically, by placing his sitters in a controlled -- and in Penn's case oftentimes confining -- environment. He loves control because it allows him to reach for the ideal of beauty.

You can almost see Penn reaching for the ideal throughout the range of subjects in his show, which includes elegant models wearing the latest Paris fashions, tribal peoples decorated with masks and mud, full-figured nudes, literary lions and celebrated artists, urban tradesmen, street trash, and still lifes made of metal blocks, skulls and bones.

At Vogue, Penn long played Plato to Richard Avedon's more mercurial Aristotle. Avedon sought to comprehend humanity by acquiring and sorting evidence of its manifold existence; beauty to him was an end, not a given. Penn seems to have started with a sure sense of what beauty is and then embarked on finding it in unusual places, from the fierce visages of warriors in New Guinea to cigarette butts and smashed paper cups plucked from the pavement of Fifth Avenue. One could even say his famous fashion images are essentially potboilers: What could be easier for Penn than making beautiful images of beautiful women wearing beautiful clothes?

"Irving Penn: Platinum Prints," organized by Sarah Greenough, is occasioned by the artist's gift to the National Gallery of 102 photographs and collages, most of which are on view in the exhibition. The prints represent Penn's labor of love since the mid-1960s, when he decided that conventional printing, both in reproduction on the magazine page and with commercially made enlarging papers, did not do full justice to his work. Working weekends in his darkroom away from the city, he resurrected a process used by Alfred Stieglitz, Paul Strand and Edward Weston early in their careers but later abandoned as anti-modernist.

To make a platinum print requires brushing a solution of metallic salts (platinum, mainly, but also mixes of palladium and iridium) onto a sheet of watercolor paper, drying it, and exposing the dried sheet to a negative the same size as the final image. Penn thus was required to make enlarged negatives of his best work, discover the right formula of metals for each image, and often to coat, expose and develop the paper multiple times to build up the density to a level that gave the print a full range of tones. Skill and persistence are required in equal measure.

To say that the results can be exquisitely beautiful is almost an understatement. Looked at closely, the pictures reveal details unseen when they were published in Vogue, like the texture of the fabric in a Balenciaga dress worn in 1950 by Lisa Fonssagrives-Penn, a model as well as the photographer's late wife. The ratty rug Penn used as a device in his great 1947 portrait of George Jean Nathan and H.L. Mencken appears even rattier in platinum than in a conventional silver print.

The effect is perversely delicious.

Lingering modernist purists may protest that these platinum prints look less like photographs than . . . well, prints. They have a toothy appearance and brown tonality that brings to mind photogravures of the sort that Stieglitz published in his magazine Camera Work in the early 20th century. A few seem literally inky, in particular a heavily shadowed print of "Rock Groups," a Summer of Love portrait of the bands Big Brother and the Holding Company and the Grateful Dead. But in an age when digital printing has made variety the spice of contemporary photography, the platinum look seems neither objectionable nor particularly radical.

The same could be said of the selection of images on view. Those familiar with Penn's career, either from retrospective exhibitions in 1984, 1990 and 1997 or from books such as 1991's "Passage: A Work Record," will find themselves among friends here, since most of the pictures can be counted among the photographer's greatest hits. About half of them also can be found in the 120-print collection of "master images" that Penn donated to the Smithsonian's American Art Museum and National Portrait Gallery in 1987. (The platinum prints were produced in limited editions of from four to 65 copies, which accounts for the duplications.) There's no evidence in the show of Penn's great work in color, of course, unless you count the platinum prints that were made from color negatives.

The National Gallery's rationale for its selection is impeccable, however. Each of the 85 prints in Penn's donation (70 of which are on view) is represented in partial form in one or more of the 17 collages known as "Platinum Test Materials" that the artist fashioned in 1989.

These collages, 12 of which conclude the exhibition, are essentially assemblies of what darkroom workers call test strips, small fragments of pictures used to sample the possibilities of exposure and development. Print quality ranges widely in the individual samples, some being so pale they seem faded, indicating that Penn's interests lay elsewhere.

In her essay for the exhibition's catalogue, curator Greenough suggests that these collages are interesting in part because of the new relationships they set up among pictures. Masks, for example, figure prominently in one that includes both New Guinea mud men and the cartoonist Saul Steinberg. More important, she suggests, the collages are fragmentary and imperfect, thus marking a new stage in Penn's lifelong quest for perfection. "By embracing the vagaries of time, aging, and decay," she writes, "Penn made the 'Platinum Test Materials' meditations on the life of art."

There are other ways of interpreting these strange objects. For one, they have the effect of creating new pictures cropped from larger ones.

Janis Joplin appears solo, severed from her Big Brother band. George Balanchine also does a solitary turn without his distracting colleagues from the Ballet Society. Also, seeing Penn's handwritten notations on the margins of some test images, taken together with a dismal lack of strong tonalities in many of them, serves to remind us how difficult a feat it was to make the final prints so convincing.

As if to underline this thought, several finished prints are hung among the collages in which they are found as fragments. If it was an overall goal of the show to make the platinum test materials seem important as autonomous works of art, this was a bad idea. But it should not detract our attention from the very good idea of adding the art of one of our greatest living photographers to the collection of one of our most respected museums.

Irving Penn: Platinum Prints will remain on view in the photography galleries of the West Building of the National Gallery of Art, Fourth Street at Constitution Avenue NW, through Oct. 2. For information call 202-737-4215. The gallery is open Monday through Saturday 10 a.m. to 5 p.m. and Sunday 11 a.m. to 6 p.m. The exhibition is supported by Merrill Lynch, the Trellis Fund, and the Ryna and Melvin Cohen Family Foundation.

Irving Penn's "Three Asaro Mud Men, New Guinea," 1970 -- one of the platinum prints in the National Gallery exhibition.Irving Penn ventured far from the New York runways for pictures such as this portrait of Cuzco children in Peru in 1948.Penn photographed the top artists of his time, including Picasso in 1957.Penn captured the breathtaking beauty of his wife and her Balenciaga dress.