Join one of the most influential artists of our time as he investigates the painting techniques of the Old Masters. Hockney's extensive research led him to conclude that artists such as Caravaggio, Velázquez, da Vinci, and other hyperrealists actually used optics and lenses to create their masterpieces. In this passionate yet pithy book, Hockney takes readers on a journey of discovery as he builds a case that mirrors and lenses were used by the great masters to create their highly detailed and realistic paintings and drawings. Hundreds of the best-known and best-loved paintings are reproduced alongside his straightforward analysis. Hockney also includes his own photographs and drawings to illustrate techniques used to capture such accurate likenesses. Extracts from historical and modern documents and correspondence with experts from around the world further illuminate this thought-provoking book that will forever change how the world looks at art. Secret Knowledge will open your eyes to how we perceive the world and how we choose to represent it.