The best photographers succeed at freezing highly specific instants — arresting the flow of time and isolating fragments that refine and define it. Richard Avedon, who was one of the best of the best, defined whole eras of our visual culture through his camera lens. This retrospective at the Norton included more than 150 photographs he took for Harper's Bazaar, Vogue, and the New Yorker (where he was, amazingly, the first staff photographer). The focus may be fashion, but the exhibition and its hefty catalog handily transcend that rarefied world to preserve glimpses of crystallized history. Starting on location in the 1950s and later moving into the studio environment, Avedon rightly realized that fashion isn't just about the clothes; it's about the personalities that inhabit them, and over the course of decades, he mastered the art of distilling personality to its ineffable essence.