In 1970 I began taking photographs whose subject matter was photography itself, a sort of analysis of the operations of photography aimed at identifying its basic elements and their intrinsic significance. For instance, what is a sensitive surface? Why using a telephoto or wide-angle lens? Why do you choose a certain format? Why making enlargements? What relation exists between a photograph and its caption? And so on. All fundamental subjects of every photography manual but seen from the opposite side, that is by a seasoned professional with twenty years of experience, while manuals are usually addressed to and read by beginners."
Source: Ugo Mulas