LOS ANGELES (Reuters) – After bringing J.R.R. Tolkien's "The Lord of the Rings" trilogy to life, filmmaker Peter Jackson is back in the world of Middle Earth with the author's prequel, "The Hobbit." The three-film series is due to open in U.S. theaters on Friday with "The Hobbit: An Unexpected Journey." The Oscar-winning director, 51, told Reuters about the 3D film, including the 48 frames per second (fps) format he used, which was widely debated by fans and critics. Q: You originally intended "The Hobbit" to only be two parts. …