Q. I am a big fan of the movie APOCALYPSE NOW. I have a copy of the screenplay and the DVD of the movie. I watch it over and over again and read the screenplay over and over again. Don’t feel bored.
I noticed, that the screenplay although written by F.F. Coppola himself is different at many places. I don’t understand what was the need for that?
The movie can change from the screenplay for a number of reasons. Scenes may have been cut in editing. Or new scenes may have been shot during editing -- Woody Allen's opening monologue in ANNIE HALL, for example.
You may have an earlier draft. You might have a "production white" without the colored change pages issued here and there over the course of the shoot as locations became available or unavailable, actors had heart attacks, got fat, shaved their heads or sets were destroyed by typhoons. For that matter, on APOCALYPSE NOW, there may not have been colored change pages issued for everything Coppola did. That shoot was famous for the amount of improvisation and chaos, with Coppola improvising stuff on set, letting actors improvise lines (particularly Marlon Brando), and generally shooting massive amounts of footage to see what it might look like. Coppola himself said, "We were like the US in Vietnam. We had access to too much money, too much material, and little by little, we went insane."
Directors often change writer's drafts, but I'm not sure they change less when they're directing their own work. You see the script differently when you're trying to shoot it. You find yourself cursing the stupid writer even when that's you. (Later, in the editing room, you may be cursing the stupid director.) And a director may feel particularly free to change his own stuff because he knows exactly why he wrote what he wrote and he's confident he can do better.