The genius of Jane Bown, the Observer’s veteran photographer, is making portraits snatched in five minutes incredibly powerful. Her secret weapon seems to be the fact that you could mistake her for a sensible headmistress, with her severe bob, and she has famously arrived on shoots with carrier bags full of shopping. Maybe that’s how she caught Mick Jagger unguarded, his head back laughing, for once not posing. Or Margaret Thatcher fussing with her hair. Now in her eighties, Bown doesn’t give much away in this doc. What you want to know is what her subjects were really like. In a newspaper interview she called Paul McCartney a ‘bit pompous’. But you’ll get no gossip here.