Shooting the honeymoon scenes in Breaking Dawn - Part 1 with Kristen Stewart, widely believed to be Pattinson's girlfriend, took extra work because of fans' expectations for the previously celibate on-screen couple.
R-Patz said: "It's more an abstract idea of living up to expectations because you don't know what the expectations are. Especially with the honeymoon stuff, it's just in people's imaginations.
"You never really think about the reality of what people's expectations are, you just try and make it good. And if you like it, then hopefully other people will like it."
Shot back-to-back, the first of the final two Twilight films, with the second part to be released in November 2012, sees Bella (Stewart) and Edward (Pattinson) taking their relationship to the next level.
"Breaking Dawn begins with preparations for Bella and Edward's wedding and the chaos that ensues on their honeymoon, and the inevitable downfall that always happens in Twilight movies," Robert said.
"The wedding scene is a relatively momentous moment for the series. I think Edward's proposed to her about 50 times now, so it's been building up and building up. Edward's excited. He's always been obsessed about marriage. I think it's one of the first points of stability in Edward and Bella's relationship."
The Twilight Saga: Breaking Dawn - Part 1 opens in cinemas on November 18. See stills from the film in our Slideshow below...