 For example Porta’s experiments with the construction of parabolic mirrors made from glass resulted in the invention of an improved camera obscura that—in theory at least—had the potential to produce images that were not upside down. Porta recommends this artifact, a combination of a convex lens and a concave mirror, for setting up theatrical shows. He uses the same setup of lenses and mirrors for his spy-glass. This telescope became a very important tool for astronomers during the scientific revolution. Yet, in Porta’s day, telescopes were usually considered to be instruments for image-making rather than tools for measuring the positions of stars (Dupré 2007, Reeves 2008, Dijksterhuis 2017).