Camera obscura. Despite its conversion into the hippest museum in London, the Tate Modern’s massive ugly building, unmistakably an old power station, could otherwise be one of Blake’s dark Satanic mills. In that guise it’s the perfect setting for three rooms lined with photographs by Diane Arbus. There would seem to be nothing new to say, or think, about Arbus’s scalding vision. She roamed the ordinary New York of commuters and shoppers, and yet somehow simply to have her eye settle on strangers transformed them.