Until 1947 the word magnum described a large wine bottle. In April of that year it took on a second meaning. Accomplished photographers Robert Capa, David Seymour (Chim), Henri Cartier-Bresson, George Rodger, and William and Rita Vandivert met in the penthouse restaurant of New York's Museum of Modern Art. They resolved to form a consortium which would protect their ownership of photo negatives (then a startling idea) and provide them with control over the editorial use of their photographs, including sales to other countries. Perhaps thinking of the flow of champagne which rewards victories,...