To the public, James Cameron is a director of top-grossing movies who moonlights as a deep-sea explorer. Cameron might see it the other way around.

With a team of engineers in 2002, he dove down 16,000 feet to explore the wreck of the German battleship Bismarck. The dive prompted him to think about the possibility of going even farther, to the deepest part of the ocean: the Mariana Trench in the western Pacific, at more than 35,000 feet.

Hoping to call attention to the need for more deep-sea research — and possibly to collect some samples — Cameron embarked on that journey himself. An arduous undertaking that included a tragedy along the way, the 2012 expedition is the subject of the documentary Deepsea Challenge 3D. But the very existence of the documentary required developing cameras up to the challenge of such a deep dive.

Going underwater

Since beginning his explorations, Cameron has worked on ways to document them visually. He started the company Cameron Pace Group with his engineering partner, Vince Pace, to design 3-D film cameras. But for this documentary film, Cameron planned to spend time in front of the lens, diving in a minisubmarine for the solo part of the journey, and so he enlisted others to direct: Andrew Wight, John Bruno and Ray Quint.

Bruno and Wight, friends and colleagues of Cameron’s, had worked on previous deep-sea expedition documentaries with him, and Quint directed the postproduction and editing phase of the film. On a number of test dives, problems arose with the submersible: The pilot’s sphere overheated, and electronic glitches interfered with the sub’s functions. Rough seas and weather complications made it more difficult to find the right time to launch.

Then there were the cameras, on the interior and exterior of the submersible, that had to be compact. On prior deep-ocean shoots, Cameron and his team used 3-D cameras that weighed close to 300 pounds each. But that kind of weight would have thrown off the balance and been too much for the submersible to handle.

“Those cameras we started building almost two years before the expedition,” Cameron said. “We called it, not too creatively, the minicam, that was built from the sensor up. The whole idea was to have it be as tiny as possible.”

Advanced technology

John Brooks, the vice president for creative services at the Cameron Pace Group, helped with the design. The team started with a small camera that had limited optics and a fixed focus and rebuilt it to suit their needs. “We had to build motor systems to drive the focus, so that it could adapt to situations and be somewhat controlled,” Brooks said.

To film in 3-D, two of these modified cameras were put together and operated as one 3-D unit. “From inside, I could turn the camera around and shoot back and look at the whole sub,” Cameron said. “I could see what its distance was above the bottom. I was essentially shooting selfies the whole time.”

Cameron also brought cameras into the submersible, including a 3-D one pointed at him that he used as a kind of video dive log to give colleagues on the surface a constant status report.

In the end, Cameron made it down to 35,787 feet. He understood the dangers, but his exploratory desires won out.

“All of my nervousness about the dive was before, like the day before I’d stop and think about it for 10 minutes,” he said. “But when I was there and closing the hatch, I was just excited to see what was down there, like a kid in the car going to Disneyland.”