I'd like to report that the 3-D used in the new "Narnia" movie is simply divine, but that wouldn't be true, and I wouldn't want Aslan on my case for fibbing.

The truth is, "The Chronicles of Narnia, Voyage of the Dawn Treader" is one of those postproduction 3-D conversions - competently done, as far is it goes, but it doesn't go very far.

Talk to anyone who's done really good 3-D - James Cameron or Zack Snyder - and they'll tell you that unless you're creating shots for 3-D and shooting in 3-D, you're not giving the audience a product that justifies the premium they're asked to pay.

True enough. If you drop your glasses during "Dawn Treader," you'll see long stretches of what is essentially a 2-D movie, with intervals of converted 3-D. I don't think the movie would suffer at all at a 2-D venue, if you want to save some money.

And provided you keep your expectations low. Part three lacks the scope, ambition and execution of the first two in the series (it has a new director, and has been handed down to a new studio).

Some of these limits are imposed by C.S. Lewis himself. By this point in the saga, the "Narnia" author had winnowed half of his protagonists. The Pevensie children lose access to the magical land of Narnia as they mature, and so the oldest boy and girl have only cameo roles here.

In "Voyage," the youngest, Edmund (Skandar Keynes), and Lucy (Georgie Henley) return with a bratty, nonbelieving cousin (Will Poulter) to Narnia, where they help Caspian (Ben Barnes) protect his kingdom by recovering magical swords that keep the forces of darkness at bay - all accomplished during an arduous ocean voyage on trackless seas. (What's with the English and the swords of destiny? Even J.K. Rowling found it irresistible.)

They run into magicians, invisible men, slavers, dragons and a green malevolent mist, but mainly the mission is imperiled by threats from within. Along the way, Edmund and his sister face temptation by various deadly sins, threatening to break bonds of fellowship that keep Narnia whole.

Edmund is tempted by power, a lust for gold. His sister by vanity and envy. I suppose lust would be too much to ask for, given the PG rating, and the generally wholesome nature of the franchise.

This all comes to a head as Caspian and company arrive finally at the site of the seventh and final sword - Dark Island. The first two "Narnia" installments aspired to epic finales but Dark Island sounds, and looks, like something out of Scooby Doo movie, and its concluding sea battle is punchless.

Again, some of this is imposed by Lewis' narrative. There is no physical villain in "Voyage" - not even a flaming eye - a very tough obstacle for a movie to overcome. The Pevensies' enemies spring from their own fears and imagination - Edmund is unable to suppress his thoughts as they near Dark Island, where fears take physical form, and so is conjured a serpent.

Shades of "The Tempest." And "Ghostbusters." Edmund's sea monster is a rip-off of the Kraken from "Clash of the Titans," but at least it's not the Stay Puft marshmallow man.