Greifswald 2024 – scientific programme

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GP: Fachverband Geschichte der Physik

GP 7: Instruments and Exhibitions

GP 7.1: Talk

Wednesday, February 28, 2024, 14:00–14:30, ELP 3: HS 2.33

On a 17th Century Telescope Lens Grinding Machine — •Wolfgang Engels — HistEx GmbH, Germany, Marie-Curie-Str. 1, 26129 Oldenburg

Some years ago, a telescope was discovered during excavations in Delft that could originate from the first half of the 17th century. The instrument is suggested to represent a surviving sample of one of the oldest in the Netherlands. The principle of these terrestrial telescopes is the use of a planoconvex objective lens and a planoconcave eyepiece. Surprisingly, the very unusual shape of the planoconvex objective lens of the find corresponds nicely to a grinding method that was suggested by the Capuchin monk Anton Maria Schyrleus of Rheita in 1645 (Oculus Enoch et Eliae...). The polished curvature of the actual objective lens is centred on a piece of flat glass from which it was cut, leaving the surrounding edge rough and unpolished. Rheita claimed that his apparatus was designed to machine both spherical and hyperbolic planoconvex lenses. Based upon Rheita's publication, the machine has been replicated and some lenses have been produced. To date, no finds of early aspherical lenses are known, but further finds of spherical lenses with the typical shape now indicate that Rheita's processing method could have been used on a large scale.

Keywords: Anton-Maria-Schyrleus-of-Rheita; telescope-lens; lens-grinding-machine; Oculus-Enoch