Chris Weitz, the director and writer of The Golden Compass film, has talked about his reasoning behind chopping the book ending off of the film and passing it onto the start of the next film, The Subtle Knife.

He reveals that the author Philip Pullman is perfectly find with the ending not following the novels, and that the only disappointed ones may be the fans of the novels.

Originally they shot the film ending as per the novel, but they discovered that this was not the way to go, presumably in test screenings. Chris Weitz talks about that over at Sci Fi Wire.

“We shot the last three chapters of the book, which are really quite ambiguous in the ending and quite harsh and dark...It became clear that audiences who were not familiar with the books were confused and appalled by the end of the movie, and in order to protect the character of these last few chapters, I thought, 'Well, it can work at the beginning of a second movie.'”

Apparently Weitz decided to end The Golden Compass on a cliffhanger rather than the way the novel ends, and he's more concerned about the entire story told throughout His Dark Materials rather than the single novel.

Well there's no reason the film should follow the novel, especially when it is so altered anyway. I still think that this film is going to be a smash no matter what, despite any religious interpretation or how it ends. It looks set to kick start a new fantasy franchise that will run for quite a few films.