This summer, you can see the largest New York exhibition ever put together about local post-war photographer Diane Arbus. For "Diane Arbus: Constellation," Park Avenue Armory has amassed more than 450 Arbus photographs. Curator Matthieu Humery and photographer Neil Selkirk, a former student of Arbus and the only person allowed to make prints from her negatives, talk about the exhibition, on view through August 17.