 Popular, operetta style costume films like "The Blue Danube", "The Bohemian Dancer", "Dancing Vienna", "Mariett Dances Today" brought Lya Mara and Zelnik enormous success in Germany and beyond.Several of his collaborators, such as cameraman Frederik Fuglsang and production designer André Andrejew are perceived today as important artists of the German silent cinema.Upon the introduction of sound film, Friedrich Zelnik became the first director in Europe to postsynchronize a movie, "The Crimson Circle" (1929), using the DeForest Phonofilm sound-on-film process.