The two major types of optical telescopes in use today trace back to the time of Galileo and Newton. They don't trace back to either Galileo or Newton, however. They trace back to Johannes Kepler and two Roman Catholic priests, Christopher Scheiner and Laurent Cassegrain. The involvement of church in these important developments was not out of place. It is no coincidence that two telescope designs in common use today are named after Catholic priests (Cassegrain and Mersenne) or that another Catholic priest (Rheita) is credited as the originator of the terrestrial telescope.
Advances in optics and telescope construction during Galileo's lifetime set the stage for the future of the telescope (see Timeline of Galileo's Contemporaries) . Oddly, Galileo was not involved in any of these advances. Galileo's preferred design was a dead end. It was dropped by astronomers shortly after his death. Galileo's is important because he made the use of telescopes respectable in science. He was also able to make superior telescopes for his time. Galileo's environs gave him an advantage. Florence had been an important center for lens-making since the late thirteenth century (see Timeline of the Telescope Year:1289) and Venice was also noted for lens-making. Galileo would order hundreds of lenses at a time and select the best to make his telescopes. Beyond these two achievements, it is difficult to name one advance made by Galileo in the theory or construction of telescopes that is in use today. That is not true of the church scientists of his day; especially the Jesuits.
The scientists who had the greatest influence on the future of optics and telescope construction from Galileo's day were Johannes Kepler, Rene Descartes, Wilebrord Snell, Father Marin Mersenne, Father Bonaventura Cavalieri, Father Christopher Scheiner and Father Christopher Grienberger. The first three developed a theoretical foundation for refraction and reflection that would be built upon in the following centuries. The four fathers made contributions that are still in use today. Fathers Marin Mersenne and Bonaventura Cavalieri together would propose the basic geometric shape that would be used in modern reflecting telescopes (see Reflecting on History). Father Christopher Scheiner, a Jesuit, would be the first to construct a modern astronomical telescope, using theory proposed by Johannes Kepler. Christopher Grienberger, another Jesuit, proposed an advanced method of mounting telescopes that made it easier to follow objects as the arc through the sky. Father Nicolo Zucchi, another Jesuit, demonstrated that creating telescopes out of lenses and mirrors was possible. This was in 1616, 50 years before Newton's famous reflecting telescope. He was the master craftsman who also built refracting telescopes for Johannes Kepler (see Jesuits and the Telescope). The early adoption of the telescope by Jesuit scientists might explain why 35 lunar craters are named after Jesuit scientists (see Jesuit Lunar Craters).
The advances in telescope making continued in the decades after Galileo's death. The lenses of Giuseppe Campani have spherical curvatures as good as can be made today [_1_] . Giuseppe Campani was first noticed when he and his brother, Matteo (a Catholic priest) entered their telescope in a competition against the greatest telescope makers of the day. The Campani telescope won. Campani and his most famous competitors were very secretive about their methods and tools. It was left to a Capuchin Monk, Cherubin d'Orleans, to spread knowledge of the craft of telescope making. Cherubin d'Orleans wrote two important works on optical instruments and optics, La Dioptrique Oculaire and De visione perfecta. De visione perfecta documents his invention of the binocular microscope. La Dioptrique Oculaire included detailed descriptions of the tools and techniques involved in the manufacture of lenses. The monk's work continues to impress today : 'These descriptions are so good, and show such thoughtful personal knowledge of the subject, that they would be suitable to place in the hands of an optical apprentice today' [_2_] . The lathes he used for grinding and polishing were very sophisticated. An image of one of Cherubin D'Orleans lathes is shown below (modified from here). Other priests from the time who published important works on telescope construction were Niccolo Zucchi and Anton Rheita.
For the last one hundred years, almost all of the largest optical telescopes have been Cassegrain reflectors. Father Laurent Cassegrain, a French priest and contemporary of Isaac Newton and Cherubin D'Orleans, was the first to propose this popular design. In an ironic twist that is so common in history, Isaac Newton was one of the leading critics of the young priest's design. Here is what Newton had to say about the Cassegrain design:
You see therefore, that the advantages of this design are none, but the disadvantages so great and unavoidable, that I fear it will never be put in practise with good effect [_3_] .More information on the early history of the reflecting telescope is found at Reflecting on History.
Church scientists from the 17th century made very important contributions to the early development of the telescope. They are rarely mentioned. The narratives on 17th century science focus on the story of two great scientists, Galileo and Newton. These narratives commonly portray the church as "battling" science. The narrative depends heavily one event, the Galileo Affair. It is ironic that the contributions of the church scientists to the history of the telescope outlived Galileo's. Galileo's preferred design of telescope ( the Galilean telescope) was largely discarded by astronomers within a decade of his death. It was replaced by the Keplerian design, championed by Father Christopher Scheiner.