After breaking all-time box-office records with both "Titanic" and "Avatar," James Cameron set out to break a more personal record in 2012: diving 35,787 feet to the bottom of the Mariana Trench, the deepest part of the world's oceans. His journey is chronicled in a new documentary, "JAMES CAMERON'S DEEPSEA CHALLENGE 3D."

Yes, the title is in all capitals, per Cameron's instructions. Well, the man didn't get where he is by being laissez-faire, and he certainly doesn't do things by halves. On this film, he is producer, narrator and subject. (The directors are John Bruno, Andrew Wight and Ray Quint.) "DEEPSEA" may not appeal to the widest audience, but it's a sometimes stirring story about one man's determination to make a dream come true.

And no ordinary dream at that. Cameron, a lifelong diver, tells us the Mariana Trench is so deep that you could stack four Empire State Buildings atop Mt. Everest "and still not break the surface." To touch its floor, he built a pressure-resistant steel sphere -- so small inside that it squeezes him into a nearly fetal position -- which attaches to a submersible vehicle. Assisted by a large team, Cameron spends much of the film making increasingly deep test-dives. Some are plagued by malfunctions and system shutdowns that drive home the very real danger of failure.

"DEEPSEA" flags when it gins up TV-style drama (will the crew be ready for the next dive?) and cranks up the anxiety-provoking score. More compelling is the technical nitty-gritty: the smelting of the sphere, the workings of the robotic arms, the stop-watched emergency drills. There's also some beautiful underwater photography, and a touching moment when the filmmaker puts down his camera and insists on looking through the window with his own two eyes.

Though "DEEPSEA" sometimes feels like a vanity project, Cameron comes off as genuinely invested in science and knowledge. His dive resulted in the discovery of 68 new species, according to the film. "DEEPSEA" is dedicated to Wight and cameraman Mike deGruy, who died during filming in an unrelated accident.

PLOT The blockbuster director James Cameron documents his dive to the bottom of the Mariana Trench.

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LENGTH 1:30

PLAYING AT Stony Brook 17 and Roosevelt Field 8 in Garden City.

BOTTOM LINE Low on dramatics, but an intriguing chronicle of a man determined to make a lifelong dream come true.