National Geographic photographer Vincent Musi has been super as Master of Ceremonies, giving his job a right mix of humor and gravitas. Yesterday, when he introduced William Albert Allard, he had a good line: "When Bill sets foot in a story, he owns it." Today, with Sally Mann about to talk, he has no similarly punchy line -- even seems a little tentative. After all, Mann is really the polar opposite, artistically speaking, of an Allard or of any Geographic photographer, Musi included. Making pictures related mainly to her own life and children, at or near her family farm in Lexington -- just over the mountains and a little south of Charlottesville -- Mann looks inward while Allard looks out. (From the pictures, her place is like no family farm I've ever visited, but that's another story.) Yet both photographers make pictures that are keenly observed, uniquely theirs, and totally about themselves.