Newly developed technologies in the filming of 3D movies allow it to be seen at any theatre. Also, apparently the effects are much more natural feeling. We'll find out, I'm sure!
From Entertainment Weekly:
Another year, another ''Spy Kids'' movie. but this time, something's different: There's a new dimension to all the little-league espionage. ''I always wanted to do a 3-D movie,'' says writer-director-editor-composer-caterer Robert Rodriguez. ''I wanted to make 'From Dusk Till Dawn' in 3-D. But it was going to be cumbersome, so we ended up abandoning that idea.'' Thanks to advances in high-definition digital moviemaking, there's nothing cumbersome about 3-D now: Rodriguez has used it to put the Cortez siblings, Carmen and Juni (Alexa Vega and Daryl Sabara), into a dangerously immersive videogame designed by yet another evil genius, this time played by Sylvester Stallone. ''He made a video for his kids [while he was on set],'' Vega recalls of the erstwhile Italian Stallion. ''He said to them, 'Look, I'm doing a kids' movie -- something you can actually be proud of me for.' He had Daryl and myself come on and say, 'Listen to your father!'''
Since the 3-D process is instantaneous, the cast could see the final product right after Rodriguez called cut. ''He sets up this screen, and you'd put on these glasses and look at yourself in 3-D,'' Vega says. What's more, the effect won't require reconfiguring conventional movie projectors, ensuring wide distribution. Once audiences slip on their glasses, they'll see a beefed-up, superenhanced...Ricardo Montalban? ''He rides a giant mech-bot,'' Rodriguez says, divulging a bit of plot, which involves the actor (who returns from the previous film to play Carmen and Juni's wheelchair-bound spy grandfather) entering the game to help Juni rescue Carmen from digital imprisonment. Inside the game, he becomes spry and Khan-like.