Photographer Barbara Nitke spent several years during the 1980s on the sets of various adult movies being shot in New York City, capturing the goings-on both in front of and behind the camera. The result is her book, “American Ecstasy,” a revealing visual document of porn’s “Golden Age.” While Nitke’s sometimes explicit images features such stars of the era as Ron Jeremy and Nina Hartley, the focus of her work is on the process of filmmaking itself, providing views of actors in repose between takes, as well as shots of directors and other crew members interacting with the talent. It’s a nostalgic, if demystifying, look at adult entertainment in the years before the internet transformed the industry into an all-pervasive, global behemoth.