The essay deals with Algarotti’s teachings on optics and painting. It explores Algarotti’s art expertise and his sojourns at European aristocratic courts. A central role in Algarotti’s texts is played by Venice as well as by the camera obscura technique. Algarotti is interested in the fictional part of human vision as well as in architectural fantasies. Thus, he expands the rationality of the Enlightenment with a theory of illusionary formation.