“Sanctum” came together when Andrew Wight, a longtime Cameron friend and collaborator, decided to make a movie about a group of trapped cave divers using the same tools and techniques they deployed on Cameron’s documentaries.

“Sanctum,” on the other hand, was conceived from the start in 3-D, and shot to take full creative effect of the tool. While there have been a handful of low-budget 3-D films, such as last summer’s “Piranha 3D,” most have been after-the-fact conversions designed to take advantage of the higher ticket prices the format commands. The story and the emotional dynamic, however, can sometimes seem secondary to the filmmakers’ desire to show breathtaking underwater shots, such as characters navigating a claustrophobic tunnel or floating ethereally as though in a giant human aquarium.

As the dangers mount and claim the lives of many on the team - think “Ten Little Indians,” only with natural disaster as the culprit - Frank and Josh must work through their issues if they are to survive. The film tells the story of veteran cave diver Frank (Richard Roxburgh) and his alienated son Josh (Rhys Wakefield) who wind up, along with a larger diving team, trapped far below the surface when a freak storm hits during an expedition. “Sanctum” essentially asks: Is the z-axis element enough to get the filmgoing public to embrace a movie in a well-worn genre with no well-known actors and few other obvious selling points?

But the movie is the lowest-budgeted feature that Cameron, who serves as its executive producer, has been involved with in more than 25 years, and it’s an important test of his belief that 3-D can be as effective in an intimate, emotional story as it is in a grand epic. Life and death are not quite at stake when “Sanctum,” a modestly budgeted ($30 million), 3-D, cave-diving adventure comes out in theaters on Friday.

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