When Francis Ford Coppola's first major 3-D film, "Twixt," premieres next month at the Toronto Film Festival, audiences will be provided with 3-D glasses, but they aren't supposed to wear them for the whole movie. The legendary director of "The Godfather" movies, mindful that the funny spectacles can be uncomfortable for some viewers, decreed that an image should flash on the screen telling the audience when to put them on and take them off.

Three-D technology is at a critical...