On an evening in December, 1980, the photographer Tseng Kwong Chi gate-crashed the party of the year: the gala at the Metropolitan Museum of Art. It was the opening night of “The Manchu Dragon,” an exhibition (organized by Diana Vreeland) of Chinese costume from the Qing dynasty. Tseng used a medium-format camera to photograph the arriving guests. An era’s tony milieu pauses, flash-lit: an amused Yves Saint-Laurent, Halston in high spirits, a quizzical William F. Buckley. Nancy Kissinger turns up in the same Adolfo dress as two other women—but nobody looks embarrassed. Tseng himself is also in the pictures, grinning away beside his subjects, with a cable release in his hand. And he is dressed, as he frequently is in his dandy-conceptualist art, in a plain gray “Mao suit,” which reads here as a laconic visual rejoinder to the exhibit’s lavish Orientalism.