Texas’ celebrated son Robert Rauschenberg joined the ranks of more than 150 American artists—from Robert Motherwell and Lee Krasner to Keith Haring and Sherry Levine—who have posed for the classic portraits of Timothy Greenfield-Sanders. The photographer, working in the past few years with a huge studio camera that accommodates 24- by 20-inch Polaroid film, produces images saturated with somber color. Fifty-one of Greenfield-Sanders’ portraits are on view through February 2 at the Modern Art Museum of Fort Worth.