David Hockney already achieved considerable success as an artist when he was in his twenties. In 1961 he was considered one of the most prominent artists of British Pop Art. Hockney's work has many references to folk popular culture, but he hated being placed in the Pop Art pigeon-hole. Hockney mainly painted people and places that he knew well himself; he paid particular attention to swimming-pools. From the 1980s, Hockney began experimenting with photo collages. Hockney also produced countless illustrations for books and designed costumes and scenery for the theatre.