Weston Naef sounds almost misty-eyed when discussing Kodak Tri-X, a black-and-white 35mm film first made in the 1950s and a staple of photojournalism for decades. "It was a wonderful 400-speed film," says Mr. Naef, curator of photography for the J. Paul Getty Museum in Los Angeles, referring to Tri-X's ability to capture an image in low light, known as its "speed." "And then it could be 'pushed' [chemically altered during development] to 1200, or even 2400"--meaning it could be used in even lower light. Tri-X--along with Kodachrome, Ektachrome, Fujicolor and all those other mellifluously named films--and the Nikon, Minolta and...