Ralph Fiennes took on a significant challenge when he decided to act in and direct "The Invisible Woman," a new film about Charles Dickens' relationship with his secret mistress Nelly Ternan (Felicity Jones) that opens in theaters on Wednesday.

It's only Fiennes' second effort behind the camera. The material is tough, requiring a filmmaker with a keen eye for externalizing the deep suffocation of both characters, who are restricted from acting on their love because of social and cultural pressures.

And Dickens, at once a lively public polymath and thoroughly enigmatic private man, is a strenuous part to play.

"It's hard to know where to emphasize your director's head or your actor's head," Fiennes says. "I wouldn't think I would do it again in a hurry, because it kind of messes up your head. The days where I wasn't playing Dickens almost seemed like a holiday, because the stress level is reduced so much."

Fiennes says he "tried to resist" playing the author, but "I'm afraid I just thought, 'Damnit, I'm going to do it.' "

Of course, Fiennes made his directorial debut with the Shakespeare adaptation "Coriolanus" in 2011, which is no slouch either.

The Oscar-nominated 51-year-old says he's gained "more confidence" in everything from working with his actors to editorial and camera decisions.

"Having got one film under my belt that gave me a level of something more assured about choices I was making," he says.

The movie, scripted by Abi Morgan from a book by Claire Tomalin, is really Nelly's story, Fiennes says, and it was the portrayal of the woman cast into the shadows that initially intrigued him.

He admits to a measure of "ignorance" when it came to Dickens' life beyond his writings before reading Tomalin's book.

Her work crystallized an important truth for the director-star: the story is defined by Dickens' relationship with his public as much as anything. "It's a weird, peculiar relationship, your concept of yourself and the public," Fiennes says. "It can distort your sense of yourself."