By Clark Collis
Updated April 25, 2014 at 05:19 PM EDT

The framing device of the new, 15-years-in-the-making documentary For No Good Reason finds Johnny Depp paying a visit to the film’s subject, British artist Ralph Steadman, at his home in Britain. Director Charlie Paul admits getting that footage proved a little tricky given that Steadman was initially none to keen on participating in the project at all, and Johnny Depp is, well, Johnny Depp.

“Ralph didn’t see the sense in making a [film],” says Paul. “He’s a very private man. [But] as the years went on Ralph became more and more relaxed with my presence and would say things openly to the camera and talk about what he was doing. Once those barriers were down, the floodgates were open, and the camera became invisible. I managed to disappear into the woodwork over the years, to the point where Ralph would openly talk about what he was doing and work without any awareness of the cameras, which then made the film a very open and honest and truthful account of his time in the studio.”

Depp knew Steadman through their mutual friend, the late “gonzo” journalist Hunter S. Thompson, with whom Steadman repeatedly collaborated over the years, and Depp portrayed in 1998’s Fear and Loathing in Las Vegas. Nevertheless, Paul reveals, finding a gap in the actor’s schedule so he could visit Steadman was also a long project. “It took a few years,” says the director. “My wife, the producer Lucy Paul, persevered brilliantly. But when I got those two together in the studio it was like they’d seen each other just yesterday. It was an instant and natural chemistry which instantly fulfilled the role that I needed.”

You can witness that chemistry for yourself in the exclusive clip below from For No Good Reason, which opens today in New York at the Lincoln Plaza cinema and the Angelika and then debuts in L.A. next week. You can also read an appreciation of Ralph Steadman by Johnny Depp in the new issue of Entertainment Weekly.