Speaking to reporters at the Toronto International Film Festival, Matt Damon said it was a lonely experience shooting “The Martian,” director Ridley Scott’s new movie about an astronaut who’s presumed dead after being left behind on Mars. Because Damon’s character is alone for much of the movie, the actor said he usually filmed his scenes after the rest of the cast was done for the day. “I literally just met most of the cast right now,” the Cambridge-bred actor joked at a press conference following the screening. “I asked him for another take and he said ‘Why? Do you want to waste everybody’s time?’ ” Damon said the script, based on Andy Weir’s novel, was well written and funny, so they didn’t change much. “When you get a really good script you don’t want to bronze the gold medal,” said Damon. “You just want to shut up and say the lines.” “The Martian,” which opens Oct. 2, costars Jessica Chastain, Kristen Wiig, Jeff Daniels, and Kate Mara.