 Dziga Vertov, whose "kino-glaz" ("film-eye") theory—that the camera, like the human eye, is best used to explore real life—had a huge impact on the development of documentary film making and cinema realism.The subsequent state policy of socialist realism somewhat limited creativity; however, many Soviet films in this style were artistically successful, including "Chapaev", "The Cranes Are Flying", and "Ballad of a Soldier".The 1960s and 1970s saw a greater variety of artistic styles in Soviet cinema.