This advice comes from film-maker Brian Woods, who directed The Dying Rooms, an acclaimed documentary about orphanages in China. He is one of the speakers at Harnessing the Power of Film to Change the World, a conference at London's Southbank Centre next Tuesday.
Woods told Third Sector: "This medium can have enormous impact for change and engages people emotionally in a way a press release never could. Charities that are cautious about working with documentary makers are dinosaurs and need to grow up."
The conference is organised by the Channel 4 British Documentary Film Foundation, which was set up two years ago with a £2.6m grant from Channel 4 to fund and distribute feature-film documentaries.
Charities that work with TV documentary makers rarely receive credits because of broadcasting rules. But Woods said that charities working with the foundation can both be mentioned and have editorial input.
"Smaller charities can form coalitions to make documentary films on common issues," he said. "This is not something that is available only to the bigger organisations."
One of the films backed by the foundation is Black Gold, an expose of the coffee trade, which went on general release in UK cinemas earlier this month. The film was funded by eight different organisations, including Christian Aid, which contributed between £2,000 and £20,000.