With the diffusion of the Keplerian telescope, refined techniques for constructing lenses were developed and a new professional figure emerged, that of the specialised optician, able to prepare excellent instruments upon commission. It was in Rome in particular that Eustachio Divini (1610-1685) and Giuseppe Campani (1635-1715) set up their workshops.

As reported by Carlo Antonio Manzini (1600-1677) in his Occhiale all’occhio (1660), the construction of lenses for telescopes and microscopes now passed through various stages that demanded special utensils and skilled workers. The selection of glass for the large objective lenses, the casting and lathing of special metal moulds for grinding them, the selection and application of abrasive materials for polishing them, often constituted professional secrets that accompanied by the invention of innovative optical solutions. One of these was the two-lens system - called "erector" - by means of which Campani managed to straighten the reversed images of the Keplerian telescope in elegant manner. Campani, in particular, not only sold telescopes all over Italy, but became the official supplier of the Paris observatory, directed by Giovanni Domenico Cassini (1625-1712).