British playwright Christopher Hampton adapted the Ian McEwan novel Atonement, into an acclaimed film.

Ian McEwan’s “Atonement” is one of the more celebrated novels of the decade, and one that doesn’t clearly call out for an adaptation to the screen. Looked at one way, it’s a sumptuous period drama, a doomed romance or a harrowing war novel. But from another angle it’s a cerebral meditation on the nature of storytelling and complicity, which is hard to translate into a visual language.

So British playwright Christopher Hampton had a difficult task adapting the book into the film that was released in the U.S. earlier this month. McEwan participated in the process as an executive producer, but Hampton received the sole writing credit. The lush film, directed by Joe Wright, stars Keira Knightley and James McAvoy as young lovers Cecilia and Robbie and, in its first section, newcomer Saoirse Ronan as the precocious child writer Briony.

The film has received generally strong reviews – many of them crediting Hampton for remaining faithful to the spirit and tone of the book, though some felt it was too respectful, and is an early favorite to receive multiple Oscar nominations, including one for best screenplay adaptation.

In a recent phone conversation, Hampton and McEwan talked about the book, the art of adaptation and what’s lost and found in the passage from page to screen.

Q: I don’t mean this as a trick question, but what is the ideal amount of input from the author in a literary adaptation?

Hampton: What do you think, Ian?

McEwan: I once adapted a Timothy Mo novel for Mike Newell, a novel called “Sour Sweet.” I liked it that Tim Mo was around, but not too much. That’s my guess as to how it should be: around, but not too much.

The relationship between the adapter and the adaptee, if that’s a word, is always delicate. But it’s much better for it to be an open relationship than not to communicate.

I think it helps to have done the demolition work yourself as an adapter, to become later an adaptee. This novel is 130,000 words long, a screenplay is about 20,000 words. A lot has to go. And it can be a very painful process – it’s your stuff – so it helps to have done it. The last thing I wanted to be was sort of the bad conscience of the project, where you say, ‘This is not what it said in the novel.’ There has to be a sort of freedom for the screenwriter.

Hampton: As far as I was concerned, it worked as it probably ought to. Which is to say, Ian was much more there at the beginning of the process, on the early draft, to record what he thought, and then I think he tactfully backed away as we got closer to the first day of shooting. At a certain point I had to back away: It becomes the director’s movie, and it gets its own momentum. And there comes a time with all movies where more and more people start to have input.

Q: What is the essence of the book? If you could boil it down, what was most important?

Hampton: I think it’s a story about a writer, and about a writer’s conscience. A writer’s lifelong meditation about the relationship between writing and life, I suppose. However, that’s kind of abstract for a movie. So, inevitably, as you come to make it, you find the movie tilting itself toward the more audience-friendly element of the central romance. It’s a matter of finding a balance: We didn’t want to lose the through line of the book at all. On the other hand, we wanted it to play dramatically.

McEwan: Yes, it would be hard to make a multimillion-dollar movie about the limits of literary modernism.

And there’s another thing that tilts it: You’re bound to want to cast a beautiful woman as Cecilia. That tilts it a little away from Briony, into the heart of a love story rather than a child’s overheated imagination. Cecilia in the book is a rather horsey-faced young woman. I don’t think that would be very interesting in a movie – especially, once you cast a starry girl like Keira, you’re bound to shift this more into the love affair than into an extended reflection on the dangers of a powerful literary imagination and how it can make amends for a mistake.

But I think Christopher kept that, like a long, thin unbreakable iron rod running through his screenplay.

Q: What could be changed, from the book, without damaging the film’s fidelity?

Hampton: The things we took out were things that didn’t move the story forward. Or logistical things, like we couldn’t really afford the Second World War. So that section had to be differently organized than it is in the book. When I wrote the screenplay we had the German Stukas strafing the columns of refugees and the Panzers roaring up the back, and we just couldn’t afford it. So we had to change the way we played those cards.

Q: Were there elements of the book that couldn’t be touched – without altering the film so that it wouldn’t work anymore?

McEwan: This really applies to all translations from books to movies: What you cannot do, unless you’re going to use hours of voice-over, is to tell an audience what any given character is thinking. That’s the luxury of the novel, and the strength is to give a taste of ongoing consciousness. Movies’ strengths clearly lie elsewhere, and the way to bridge that gap is, I think, in the casting.

Much of the first half of this novel takes place inside Briony’s mind, and I think one of Joe’s first brilliant moves was to cast Saoirse Ronan: I was quite swept away by her inwardness, her watchfulness, a kind of childlike solemnity that gave a sense that you were on the inside of someone’s mind.

Q: Ian, I know this isn’t your first time, but what’s it like to have something in your head for two or three years and then see it on the screen, with, in some cases, famous people impersonating your characters?

McEwan: It is very strange, but it comes about slowly, so it’s not a shock. You know what making movies is like – they inch forward. You walk around for two or three years with all of these people in your head, and they seem so entirely yours that even when the book is published it’s quite remarkable to even hear people refer to the characters by their names.

But the movie: It is very strange. It can be peculiarly distancing; you feel that it’s both yours and no longer yours. You feel that it’s got its own life, and now it’s spawned another life. It’s almost as if the movie is your grandchild – the child of your child. And having grandchildren can be a very pleasant experience, indeed. You’re not directly responsible, but you get all the fun, if I can continue this simile for a bit. The child is still the child, and the grandchild is this other thing.