Secret Knowledge - Rediscovering the lost techniques of the Old Masters.
London: Thames and Hudson, 2001.
First UK printing
This is Hockney's huge and still controversial book of art historical analysis, in which he proves to his satisfaction, that the Old Masters from the earliest days of the Renaissance, developed their extraordinary observation skills with the aid of lenses, optics and camera obscura.
This tradition was lost again with the Impressionists' use of quick studies to capture an essence and is now largely forgotten.