Although the coincidence of the burning point and the inversion point of the images visible in a concave mirror or through a convex lens was empirically known, it was extraneous to the perspectivist tradition of optics. In similar manner, the theory of images generated by a "camera obscura" was also extraneous to the perspectivist tradition. This situation created a great deal of conceptual confusion. In tracing the geometric constructions of the perspectivist tradition on paper, some mathematicians - among them Giovanni Fontana (c. 1395 - c. 1455) - believed they were constructing magic lanterns able to project images floating through the air.

In spite of this confusion, the camera obscura equipped with lenses or mirrors to erect the images opened the way to the first theoretical attempts to build a telescope. Specifically, William Bourne (d. 1583) designed a device to magnify distant objects by combining a convex lens and a concave mirror. Unfortunately, Bourne’s concept of magnification - the larger the lens, the greater the effect - led to failure. Any lens-maker would have encountered insuperable material problems in attempting to construct very large lenses.