On the Origin of the Keplerian Telescope

After more than four centuries, we still do not know the genesis of the Galilean or Dutch Telescope precisely. But even less is known about the origin of the astronomical telescope, i.e. the instrument made with two convex lenses, also known as the Keplerian Telescope, which became widely used from the second half of the seventeenth century. In his Dioptricae, Kepler (1611) described the combination either of two or three convex lenses, but he never described a telescope or made such a device. A passage in the Jesuit annual account of the year 1616 at the Tyrolean State Museum shows that this kind of telescope was in the possession of the Archduke Maximilian III, and that it was converted for terrestrial use by the Jesuit astronomer Christoph Scheiner. In his Novae Coelestium Terrestriumque rerum Observationes , Francesco Fontana (1646) claimed to have conceived the first positive eyepiece already in 1608. He also produced a testimony by the Jesuit Johan Baptista Zupus who declared to have used his new telescope since 1614. Generally, Fontana's claims were not taken seriously, but he remains the most likely candidate as manufacturer of the first Keplerian Telescope, almost contemporary with the Dutch one

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