Fans will be aware that one of Avatar director James Cameron's great passions is deep-sea diving.  Even before Titanic, there was The Abyss, in which a group of Navy SEALS found extra-terrestrial life lurking miles down on the ocean floor.

It is hardly a spoiler to say no similar revelation occurs at the climax of Deepsea Challenge 3D, which documents Cameron's quest to reach the deepest place on earth, situated in a trench in the western Pacific north of Papua New Guinea.  There is a scientific rationale for the expedition, undertaken in collaboration with the National Geographic Society.  But as with climbing Everest or going to the moon, the real point is simply being able to say that you got there at all.

Most of the film is concerned with the journey rather than the arrival, tracking the creation of an innovative rocket-shaped vessel – the Deepsea Challenger, built in secret in Sydney – followed by a series of trial dives leading up to the main event.

Diving enthusiasts will be fascinated by the technical details; for the rest of us the film is of interest mostly as a study of Cameron, who is far from a natural movie star but certainly an authentic oddball. Wiry, white-bearded, with an obsessive gleam in his eye, he recalls Captain Ahab or at least Steve Zissou, the oceanographic filmmaker played by Bill Murray in Wes Anderson's The Life Aquatic.

Cameron affects a folksy manner and encourages a we're-all-in-this-together camaraderie among the members of his team.  The fact remains, however, that he is the only one who actually gets to go on the big adventure, and that most of his associates are being paid to indulge his whims.

This includes the directors of Deepsea Challenge itself: three are credited, including Australia's Andrew Wight, who died in a helicopter crash in 2012.  This tragedy becomes part of the film's narrative, sending Cameron into a tailspin though his determination does not falter for long.

What lingers is the sense of Cameron as an essentially solitary figure, whose journey to the ocean floor is, literally, a way of getting further and further from the rest of the world.  Perhaps this impression would be different if we were allowed to see more of his wife Suzy Amis – whose gaunt look suggests an iron will to match her husband's, but who awaits his return to the surface with a glow of unmistakably genuine devotion and pride.