In 1646, Francesco Fontana (1580–1656) published his Novae Coelestium Terresriumque Rerum Observationes which includes discussions of optical properties of systems of lenses, e.g., telescope and microscope. Our study of the Novae Coelestium shows that the advance Fontana made in optics could not have been accomplished on the basis of the traditional spectacle optics which was the dominant practice at his time. Though spectacle and telescope making share the same optical elements, improving eyesight and constructing telescope are different practices based on (...) different principles. The production of powerful astronomical telescopes demanded objective lenses with much longer focal length and eyepiece lenses with much shorter focal length than the range of focal length of lenses used for spectacles, respectively. Moreover, higher standard of precision and purity of the glass was required. The transition from the practice by which optical components were chosen from ready-made spectacle lenses to lenses which were produced according to predetermined specifications (e.g., calculation of focal length) was anything but straight forward. We argue that Fontana developed the optical knowledge necessary for improving the performance of optical systems. Essentially, he formulated—based on rich practical experience—a set of rules of calculation by which optical properties of a lens system could be determined and adjusted as required. (shrink)

Summary The twofold objective of this study is (1) to identify and give a brief review of the historical development of the various designs of early (pre-1850) telescope eyepieces, and (2) to determine by measurements and calculations the axial and lateral chromatic aberrations of a number of extant eyepieces from that period in order to provide basic data on which to judge the relative quality of different eyepiece forms. Eight distinct types of eyepieces containing one to five lens elements are (...) discussed and illustrated. The second objective was addressed by measuring the focal lengths of the individual lens elements and the lens spacings in each eyepiece. The data were processed by a ray-tracing program that yields the chromatic aberration (CA) and focal length of each of the eyepieces. Twenty-one telescopes from that period were studied in this way. Similar calculations were also made using data available in the literature on several additional historic telescopes. The conclusions drawn from the data are: (1) Telescopes with Galilean eyepieces have a smaller CA than those with Keplerian or Huygens eyepieces. (2) The two-lens Keplerian terrestrial eyepieces are demonstrated to have larger axial and lateral CA than any of the other eyepiece types. (3) Calculations from examples of telescopes by Divini and Campani for which data were available indicate that while the axial CAs of the two were the same, Campani's instrument had a much smaller lateral CA. (4) Five element eyepieces were found to be better corrected for CA than the early four-lens systems that replaced them. (5) This study tends to confirm the speculation that the reason makers of early achromatic telescopes overcorrected the objective lenses was to compensate for the CA of the eyepieces. (shrink)

The Kunstkammer of the Electors of Saxony, founded in Dresden around 1560, housed one of the richest collections of tools and scientific instruments in its day. A close analysis of the optical objects in the collection in the decades around 1600 is undertaken here—in particular, their arrangement by a mathematically trained curator, Lucas Brunn, and their use in an ‘experiment’ by a distinguished visitor, Johannes Kepler. It is argued that the selection, display and use of optical objects within this collection (...) reflect a specific, playful image of optics promoted at the Saxon court.Keywords: Court collections; Optics; Instruments; Perspective; Wonder. (shrink)