In an interview with Hypable, author Veronica Roth provided fascinating details about how filming for the highly-anticipated book to film adaptation is going so far.

The Divergent author sat down with us and several Divergent fan sites to talk about her time on the set, the chemistry between Theo James and Shailene Woodley, and how director Neil Berger is spending a huge amount of time making sure the movie is loyal to the book.

For Roth, the moviemaking process is an entirely new and “really interesting” experience. “I’ve never read a script before. I was really impressed by how closely it stuck to the general plot line of the book,” she said when asked what her first reactions were.

What’s also new for the author is seeing her characters portrayed by people other than those she imagined in her head for so long. And then there’s the added benefit of watching the actors work with one another to bring the story to life. “It’s really interesting to see how the actual actor relationships reflect the character relationships. All the young initiates have a great comrade with each other.”

Those behind the camera were equally enjoying the project. From the costume designers to set builders, “everyone seems really positive and pumped up and excited to figure out the details of this crazy world.”

As for lead stars Shailene Woodley (Tris) and Theo James (Four), Roth responded with an impassioned “Yes” when asked if the two stars have the right chemistry. “When I saw the screen test, I pulled away and I went like this… [Fans herself]. It was really good! There’s a reason they cast [Theo].” Asked to describe James’ Four in four words, Roth answered: “Handsome. Intense. Sensitive. Badass.”

Despite all of this good news, Roth has been hoping the actors can bring their unique vision of the characters to the screen. “I would be a little disappointed if it was exactly how I pictured [the characters] because there’s then no re-interpretation, no new discovery. What I was most concerned about when they were casting was finding actors who could capture the internal world of the characters as opposed to exactly matching the description that I wrote. And in that sense I think it’s been really amazing because when I was watching them act I was like, ‘Yes. This is the person, you did such a great job.’ So even with people I was on the fence with, I was really swayed – at least by the end of the day.”

Roth was also comforted by the overall aesthetics of the film after having lengthy discussions with director Neil Berger. “I was worried that the overall visual sense of the movie would be a little too futuristic/sexy? Like really sleek, shiny. That’s not the world of Divergent,” she told us. “Everything’s falling apart [in the book], and I think [Neil] definitely did that. The visuals I’ve seen have been in that vein, and that’s been really exciting.”

She was very pleased by how detailed-oriented Berger is, which will come as good news to readers who want the movie to be loyal to the book. “Everything down to the little details that I saw have been so well thought out. Like, the philosophy of the world. He and I talked for hours – he asked me so many questions, things I never thought of. Like, ‘How’s commerce work in this particular faction?’ I was like, ‘I don’t know! Where were you when I was writing this?!’ So those conversations were really reassuring because he’s been so interested in every little thing.

Details sometimes have to be sacrificed with book-to-film adaptations, however, and one change that had to be made was the ages of the real life actors playing the fictional characters. While Roth admitted she was “definitely concerned” about the age gap between Woodley (21 years old) and James (28), once she saw them together she knew everything would be alright. “Seeing them all together, they definitely look younger than you think,” she told us. “I’m really happy with the maturity of the actors.”

James’ age clearly didn’t affect Roth’s thoughts on his portrayal at all. Despite the 10 year age gap between the actor and character, he was Roth’s first pick when asked which star closest matched her vision. James was followed by Maggie Q who plays Tori. “I’ve seen her on Nikita. She’s a badass, she’s already Dauntless, it’s all there.”

As for the lead star Woodley, Roth was nothing but pleased with what the actress brought to the table. “Shailene brings reality. Tris is an impetus 16 year old. She makes – she has kind of a harsh personality with some vulnerability. And I think all of the shades of what Tris is, is what Shailene is able to do. Just in very small moments too, they’re pretty subtle. Even though she’s not a tiny blonde girl, she just IS this character. She seems like a real person who’s actually having these struggles which has been – I wasn’t that surprised because I saw her in The Descendants, but.. I just didn’t think anyone would be able to do it because Tris is so dear to me.”

Divergent opens in theaters March 21, 2014. Read more from our interview with Roth…

– Veronica Roth is a Harry Potter fan and MuggleCast listener!
– Veronica Roth goes in-depth on Allegiant: Choosing a title, creating a unique story, more