Alexander Payne, director of this fall's acclaimed Sideways, has always resisted the notion that he makes dark comedies. ''When people say 'dark,' what they really mean is 'real,''' he insists. But 14 years ago, as a UCLA film school student, Payne cut his directorial teeth with a comedy he acknowledges is ''genuinely dark'': a 50-minute thesis film about a depressive photographer named Martin (Charles Hayward) who becomes psychotically obsessed with a beautiful young woman (Lisa Zane). While the film, loosely based on an Argentinean novel called The Tunnel, couldn't have been much bleaker it ends with Martin putting his beloved in a coma (ho ho!) it got Payne's career off to a bright start. Within six weeks of its first screening at UCLA, he had an agent and a writing-directing deal at Universal. Payne got some inquiries about remaking Martin as a full-length feature but wasn't interested: ''Why would I want to make the same movie twice?'' he asks. Still, while it has been seen by relatively few people at film festivals, Payne retains a special passion for Martin: ''It was one of those dream scenarios film students hope for. It was quite a ride.''