The late pop artist Ray Johnson is like the Charles Foster Kane of documentaries: When he died of drowning at age 67, he left behind a seeming multitude of acquaintances, each of whom held a piece to the puzzle that was his character. Though the missing pieces are even greater in number, it's fun to watch filmmakers Andrew Moore and John Walter try to locate a logical rationale for Johnson's odd personality and activities like renting a helicopter to drop foot-long hot dogs over Rikers Island. His collages were pretty spiffy, too, and they make stylish framing material for this rollicking real-life mystery. Luckily, a number of Johnson's survivors are or were photographers, and their elegant portraits of him offset the visual dreariness and clumsy camera work that mar their own turns in front of the lens. On the whole, the movie is as rewarding a 90 minutes as you can devote to a subject who did his best to remain eternally unknowable.