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Yousuf Karsh, the Armenian-born Canadian photographer (1908-2002), was technically accomplished, but is sometimes considered overly deferential in his portrayals of the rich and powerful, often flattering them with dramatic stage lighting. A new exhibit of a few dozen of Karsh’s images at the National Portrait Gallery—-the first of two sequential installations this year and next—-alludes to this aspect of his work when it praises his “iconic portraits of many of the 20th century’s most influential men and women.”

Indeed, Karsh’s portraits of businessmen and women in the exhibit—-images of publisher Henry Luce, cosmetics entrepreneur Elizabeth Arden, fried-chicken magnate “Colonel” Harland Sanders and Washington Post publisher Katherine Graham—-don’t seem to probe too deeply below the subjects’ prosperous surfaces.

But other works in the exhibit show flashes of something more substantial, particularly when portraying men and women of arts and letters. He captures an impish I.M. Pei standing in a doorway; a besotted, cigarette-puffing Tennessee Williams at his typewriter; an inscrutable Georgia O’Keeffe in her New Mexico home; and a placid Ernest Hemingway in a turtleneck sweater.

Karsh’s finest works, though. cannot be fully understood without some important out-of-the-frame context, which, happily, the National Portrait Gallery provides.

In one early image of President Franklin D. Roosevelt, his son James, and the governor-general and prime minister of Canada, it’s explained that the foursome posed stiffly for an official portrait (or what they thought was an official portrait) before the image shown was taken. In reality, Karsh mimicked the sound of a camera shutter when they were standing rigidly, then snapped the shutter once the men had relaxed. The resulting image is admirably casual.

The most famous of Karsh’s portraits has an even more sui generis origin. In 1941, with the war in Europe well under way, Karsh went to the Canadian Parliament to photograph Winston Churchill. Churchill gave Karsh two minutes in a wood-paneled room to make his exposure. Karsh gently objected to Churchill’s cigar, but the prime minister had just recently lit it, and he refused to give it up. So Karsh “deftly” removed it from Churchill’s possession, then made his photograph. The resulting grimace came to define Churchill’s persona and became a symbol of the ferocity of Britain’s fight for survival. Not bad for two minutes’ work.

On view to April 27 at the National Portrait Gallery, 8th and F streets NW.

Correction: The original version of this review misidentified the location where Churchill’s photograph was taken. It was shot in Canadian parliament, not British parliament. The text has been corrected.