Canaletto's Visual Cone (1697-1768): The Observational Drawing through the Filter of Kepler's Retinal Optics

Abstract

During the XVI century, Plater's scientific advancements replaced the crystalline lens theory that originated with Galeno, with a new theory focused on the retina as the biological center in the formation of the flat image. With this historical rupture, Kepler sought to articulate the Euclidian geometry, the Renaissance perspective and the new optical-physiological description through the concept of "pictura". The mathematical correction allowed for the resolution of errors and geometric variances between the visual stimulus and the representation. The reversal of the "Euclidean Visual Cone" for the "Keplerian Visual Double Cone" demonstrates a novelty in the geometry of observation. This change in the boundaries of biological vision that extend and correct, influenced the field of art, particularly through the camera obscura. The operation of the camera obscura approached the description of the mechanical eye, and allowed artists an instant projection of the visual scene. The dissemination of this optical instrument favored the accuracy of design, increased production speed and multiplied experimentation. It automated a uniformly varied observation. However, the probability of the drawing with the camera obscura depended on the draughts person's perception. The mimesis of exercise exceeded the physical projections of the visual scene. The modeling of attention, experience and motivation of the phenomenological observer produced a visual information management based on four operations: selection, compression, hierarchy and speed. Canaletto technically developed this cultural dimension. Known as a landscape painter, his vedute had, as an aid, the drawing of in situ observation. Canaletto's observation methodology pioneered in foreseeing photographic multiplication: i) carrying out successive drawings of a given site, ii) expansion of the details of a scene depicted with variability of the focal length, iii) the panoramic drawing by increasing the amplitude of the visual cone. The panoramic perspective multiplied visual cones to a high frequency distribution over the field of view, which corrected the deformation of the peripheral vision of the observer through linear perspective. The standardization of focus for camera obscura allowed acceleration in observation times and representation in the drawing. The image of the camera was influenced but the observational drawing as a customized product of Canaletto. He corrected in his drawings the scientific vision of optical geometry by way of differences in creative topography of the human vision, in which art seeks answers.