18th Century Italian: Canaletto

Canaletto (Giovanni Antonio Canal) is well established to have used a camera obscura in his early studies. It is assumed that he slavishly copied the image projected inside his tent. Geometric analysis reveals, however,that Canaletto's perspective was not geometrically accurate, implying that his use of the device was not quantitatively systematic.

Pilasters on the Ducal Palace

Counting from the center, Canaletto paints more pilasters and more arches on the far side than the near side. Architecturally, there are the same number (after accounting for the one extra pilaster and arch cropped out at right).

Reconstruction the vanishing point makes it clear that Canaletto constructed the basic perspective accurately for both the palace and the Mola. Any horizontal spacing should reflect vanishing points lying vertically above or below this vanishing point (on the yellow line).

The rear palace windows do not conform to the vertical spacing constraint, implying that Canaletto constructed the perspective, rather than copying an optical image, but did not understand the vertical constraint.

In this painting, Canaletto employs an oblique perspective view of the Ducal Palace from the Piazza San Marco, in which there are geometric decorative patterns. On reconstructing the right hand vanishing point, we find that Canaletto used an accurate projection to a single vanishing point from the floor of the piazza to the tops of the flagpoles.