The young photographer photographing the old photographer.

"It's very unusual to see a 28mm lens being used for a portrait," says Alfred Eisenstaedt, who, at 81, with 50 years of his own photographs sprawled behind him on the walls of the National Museum of American Art, knows what's unusual.

"It's a 21," says the young photographer.

"Ahhh," says Eisenstaedt, in a thick, heavy, seen-it-all Weimar Republic ahhh which might scare a more timid man into changing his lens.

"Lean forward," says the young man, not changing his lens.

"You will make me look like . . ." Eisennstaedt complains, flaring his hand in front of his face, fearing the wide-angle lens will distort him, make his face look like the reflection in the back of a spoon, his nose being nicely ample as it is, and the chin cruising like a big ship through the maelstrom of strobes, onlookers, autograph hunters, reporters and museum guards getting ready to celebrate the show and the publication of Eisenstaedt's 10th book, "Germany."

"Don't I look like a hunchback? Well, thank goodness I don't have to pose me, you pose me. Wait, I don't sit like this . . ."

"Do you want to look through the viewfinder?" says the young photographer, laying it all on the line, put up or shut up. He and Eisie, as he has been known at Life magazine since the 1930s, trade places. Eisi, photographer of Hitler, Rachmaninoff, Churchill, Clark Gable, Yehudi Menuhin, Bertrand Russell, Marlene Dietrich, John F. Kennedy, Hemingway -- "all of them, I have photographed them all," he will say -- this Eisenstaedt looks through the viewfinder at the young photographer who has taken his place on the bench in front of his pictures and says:

"You make me look like a spider in a web."

"I got the idea from you," says the young man, and finally Eisenstaedt can't argue.

He is one of the founding fathers of photojournalism, a Berlin button salesman who was a camera hobbyist until, one day in the late '20s, he says, "a man showed me I could crop and enlarge pictures -- I could leave things out I didn't want. I'd never thought of it. It was a turning point in my life. The first picture I sold, it was of a tennis player, for $3 to a Berlin magazine. I took it from 50 yards away from a little hill. And then I cropped out the tree and the bench, I just used her and the shadow. They called it 'Autumn Shadows Growing Longer.'"

That was in 1927. "I didn't know photographers could make money," he says.

No one ever had, really, photography being the province of basement chemists and hobbyists, as opposed to nowadays, when all the rich kids in the world who want to claim they work for a living say they're photographers.

And when Eisenstaedt turned full-time pro in 1929, it was very hard work indeed. Plus the basic rules of the game were still hazy.

"I didn't have an exposure meter. I didn't know what one was. I shot everything at f1.8, wide open. When I went to Assisi to photograph the wedding of King Boris of Bulgaria to the daughter of Victor Emmanuel, I carried 240 pounds of equipment. All I had were 2 1/4-by-2 1/4 or 3 1/4-by-3 1/4 cameras, and not film but glass plates, each glass plate in a steel holder.

"What a wedding that was! Mussolini would come strutting by and King Ferdinand with his long nose, he had the longest nose. When I got back, my boss said, 'Where are the bride and groom?' I was so interested in the other people I hadn't even seen them. They wanted to fire me. They were sorry to find out I was a free-lancer, I wasn't working for them."

In 1933, having photographed crowned and uncrowned heads of state, along with actresses, musicians, dancers, businessmen, street scenes, bicycle races, everything that looked like a picture, Eisenstaedt came to America to wind up at Life magazine, where n 2,500 assignments during the heyday when the whole world was saying cheese for a Life photographers, he shot 90 covers, nearly two years' worth.

And now, at 81, he has gone back to Germany for the first time, revisited the scenes of his Berlin boyhood, photographed the new Germany in its down jackets and Levis, and the old grown old -- Max Schmeling, for instance, whom he photographed when he was heavyweight champion, and Leni Riefenstahl, before she became Hitler's cinema propagandist.

Then and now. It's displayed on the walls behind him, the fine sense of composition, famous people shot just the way they wanted to look, it seems, which shows not only their glamor, but their bluff and pretense.

Anyhow: Eisenstaedt, just now, is on the other end of the camera.

"It's a one-second exposure," says the younger man.

Having tested him and found him worthy, Eisenstaedt surrenders as master photographer and decides to become master subject instead.

"That's fine," Eisie said. "I can hold completely still. Once when I was photographing Bertrand Russell I said to him: 'You have a face like stone.' Russell looked at me and said: 'A . . . crocodile . . . moves . . . very . . . slowly.'"

He laughs. He says: "I can make my face absolutely still. You want me to show you?"

And he does: this elfin man in red necktie and blue blazer, all brio with a grin that shows both lines of teeth, he freezes all this and holds his face absolutely, completely still. For seconds on end. It's wonderful. Almost alarming. The photographer, after all these years, becoming his own photograph.