More people than ever are setting up impressive home theaters with high-definition plasma displays, Blu-Ray players, and surround-sound speakers. Journey to the Center of the Earth 3-D, opening today, exemplifies Hollywood's best hope for luring people back to the theater: lots of action, big stars--and the option of full 3-D. But as the first feature-length, live-action digital 3-D film, Journey posed an unprecedented technical challenge.

Today's 3-D movies are a far cry from those of the 1950s, commonly considered the golden era of 3-D. Directors of modern 3-D films don't rely as heavily on "punch in the nose" gimmicks; their dual-camera setup relies intensively on real-time error-correcting software; and editors use state-of-the-art image-processing algorithms to remove artifacts of the stereoscopic filming process, says John Lowry, founder of Lowry Digital, in Burbank, CA, the company that digitally enhanced Journey before it hit theaters.

In addition, Lowry says, the modern projectors, screens, and glasses used in theaters have improved the 3-D experience by reducing jitter--the headache-causing motion difference between the pictures for the right and left eyes. "It's just much easier to watch 3-D today," he notes.

Most modern 3-D feature-length films have been animated, so they've allowed for a lot of computer modification of the shots. But for a live-action film, says Vince Pace, founder of PACE, the Burbank company that supplied the cameras for the film, there's the added challenge of making the filming process as invisible as possible to the actors. In other words, he says, the technology has to work: cinematographers can't be fiddling around with the camera when the action has started.

The first consideration is, of course, the camera. Stereoscopic technology has been around for more than a century, and a lot of the basic tricks are well known, Pace says. "Seventy percent of the [3-D camera] equation has been known for some time: you use two cameras, duct-tape them together, and there you go," he says. "But 30 percent is subtleties."

Pace explains that for a stereoscopic camera setup, the two lenses should be about 2.5 inches apart, roughly the distance between a person's eyes. The left camera collects information for the left eye, and the right camera for the right eye. But the lenses of two separate cameras can't be put much closer together than six inches due to their physical enclosures. The workaround that PACE and many other 3-D filming companies use is to shoot directly through one lens but use a mirror about 2.5 inches away to direct an offset image onto a second lens. The reflected image needs to be inverted and flipped before the film is edited.