At the Crossroads of American Photography examines the aesthetic and personal interrelationships of three photographers who helped define the course of American photography after Steiglitz: Frederick Sommer (1905-1999), Harry Callahan (1912-1999) and Aaron Siskind (1903-1991). Although each member of this "holy trinity" (as they were dubbed by photographer and publisher Jonathan Williams) has been honored with individual museum retrospectives, this...