When Harry Potter opens this week, will your mind’s eye blink?

‘A kind of crime against the imagination.” That’s what a recent editorial in Canada’s Globe and Mail called the upcoming film adaptations of J. R. R. Tolkien’s Lord of the Rings trilogy and J. K. Rowling’s Harry Potter series. Strong words to describe the two most anticipated films of the year. But as they fast approach–Harry Potter and the Sorcerer’s Stone opens November 16, The Fellowship of the Ring December 19–apprehension lurks, albeit alongside great excitement.

Leah, 13, can’t wait to see Harry, but she’s nervous, too. “I have [the characters] totally down to their wrinkles in my mind,” she says. (She asked that her real name not be used.) “I just hope it doesn’t change my imagination, because I’ve got a really big one–I don’t want it to limit it.” That’s the fear: that these two films, both created with special effects and obsessive accuracy that arguably make them the “realest” fantasies to ever hit the big screen, could imperil the richly imagined inner worlds of millions of readers.

Virtually real. These aren’t just any movie adaptations, after all. Both book series have sold over 100 million copies worldwide. Pleasing these fans is not just a happy byproduct of accuracy but a necessity in selling the film. And special effects haven’t been up to the challenge of Lord of the Rings till now–creatures are portrayed by humans or convincing computer graphics, not wheezy animatronics (or worse: puppets!), and the battles are reportedly astonishing. Harry, for its part, doesn’t disappoint: Hogwarts is just as Rowling described, all spires and staircases; the Quidditch matches look real enough to be live. “We’ve reached the point where it’s no longer necessary, when watching a film like the Lord of the Rings or Harry Potter, to suspend disbelief,” says Phil LoPiccolo, editor-in-chief of Nashua, N.H.-based Computer Graphics World.

The downside, of course, is if the images overpower the imagination. When children describe what they’ve read, details vary widely from child to child, says Douglas Reeves, author of The 20-Minute Learning Connection. But kids who have just seen a movie are likely to give very similar accounts. LoPiccolo’s 12-year-old daughter, for one, refused to look at so much as a still from either film, not wanting to contaminate her mental images.

But that’s assuming our fantasies of how books “look” are very defined, which will vary from person to person. “Of the characters in Lord of the Rings, I have more of a feeling for the way they look than I actually have visions of them individually,” says Amanda Cockrell, director of Hollins University’s graduate program in children’s literature. Not so for Potter and friends, whom she sees clearly. “I think we tend to form a clearer picture of people in fantasies that are essentially laid in the world we inhabit already.”

Lar deSouza, 38, a freelance illustrator, was so taken with Rowling’s books that he started sketching people and scenes in his spare time (they’re online at www.harry potterfans.net/potterica). He thinks the film has the potential to make the books more vivid. “When I get comments from kids writing to say ‘that’s just how I pictured Hermione and Neville,’ I don’t think they really do picture [them]. As an artist, there’s not a photographic process in my brain and a Xerox coming out of my hand,” he says.

Visitors to an exhibit of props from The Fellowship of the Ring at Toronto’s Casa Loma castle last week were entranced with the costumes, cutlery, pipes, books, and other artifacts. The verdict was virtually unanimous (save for one man who thought the dreamy-eyed elves looked “too out of it”): What they saw matched their imaginations. But then, fans have long used filmic imagery to help envision their favorite books. “Casting” fiction with real-world actors is commonplace. And the more cinematically inclined may shoot scenes in their heads. Michael Regina, 23, the editor of Tolkien fan site TheOneRing.net, says, “I’m rereading the books now just to see how the filmmaker in my head would do it.”

Outside Casa Loma, fans weren’t too worried about either film. “I can’t wait to see Harry Potter,” says Madeline Maynard, 17. “It might change things for the better, but if I don’t like the movie, I can just forget everything I saw.”