The revolutionary photographer Diane Arbus, who died in 1971, at the age of forty-eight, said, “A photograph is a secret about a secret. The more it tells you the less you know.” That’s not quite right, on the evidence of “Diane Arbus: Revelations,” an indeed revealing, though gratingly worshipful, retrospective at the Metropolitan Museum. Confronting a major photograph by Arbus, you lose your ability to know—or distinctly to think or feel, and certainly to judge—anything. She turned picture-making inside out. She didn’t gaze at her subjects; she induced them to gaze at her. Selected for their powers of strangeness and confidence, they burst through the camera lens with a presence so intense that whatever attitude she or you or anyone might take toward them disintegrates. Arbus’s fine-grained black-and-white film and minimalist form—usually a subject centered in a square format—act with the virtual instantaneity of punchy graphic design. The image starts to affect you before you are fully aware of looking at it. Its significance dawns on you with the leisureliness of shock, in the state of mind that occupies, for example, the moment—a foretaste of eternity—after you have slipped on an icy sidewalk and before you hit the ground. You may feel, crazily, that you have never really seen a photograph before. Nor is this impression of novelty evanescent. Over the years, Arbuses that I once found devastating have seemed to wait for me to change just a little, then to devastate me all over again. No other photographer has been more controversial. Her greatness, a fact of experience, remains imperfectly understood.