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SUMMARY:What does 'achromatic' mean? Refractions on the construction of ea
 rly achromatic telescope lenses - Michael Korey (Mathematisch-Physikalisch
 er Salon of the Dresden State Art Collections)
DTSTART:20241114T153000Z
DTEND:20241114T170000Z
UID:TALK223471@talks.cam.ac.uk
CONTACT:Dr. Rosanna Dent
DESCRIPTION:Drawing on the work of telescope collector and optical enginee
 r Rolf Willach\, this richly illustrated presentation looks at central\, y
 et previously unexamined aspects of the transition from single-lens telesc
 ope objectives to doublet and triplet lenses made by John and Peter Dollon
 d.\n\nWhereas the thorough\, detailed investigation by Brian Gee (complete
 d by Anita McConnell and Alison Morrison-Low) of the Dollond patent disput
 e focused on archival and printed sources about the innovation\, studies b
 y Willach and Duane Jaecks have concentrated on the subtle optical physics
  that distinguishes the new compound lenses from their predecessors. Still
  other work by Roger Ceragioli\, and more recently by Huib Zuidervaart and
  Tiemen Cocquyt\, has brought together archival and optical research\, to 
 generate even deeper insights into this episode.\n\nAt the heart of the tr
 ansition is the problem of chromatic aberration\, which can be stated rath
 er simply: when white light encounters a lens\, different colours come to 
 focus at different points\, causing images with coloured fringes and annoy
 ing prismatic bands. By the 1650s\, the problem was widely lamented\, and 
 a solution was desired. In fact\, many solutions were developed (both in t
 heory and practice)\, were used\, and were even advertised.\n\nBut what wa
 s the actual problem? And what did it mean to solve the problem? That is\,
  what did it mean to be achromatic? To our surprise\, the answers in the 1
 750s and following decades were surprisingly vague\; rather curiously\, re
 cent scholarship has not discussed this at length either. And looking thro
 ugh old telescopes\, as the lecturer has done for decades with his collabo
 rator Marvin Bolt\, raises serious questions about the accuracy of traditi
 onal tales. We need to broaden our analyses\, especially to avoid anachrom
 isms from colouring our historiography.\n\nWillach's latest research explo
 res\, for the first time ever\, a plausible method by which Dollond could 
 have produced achromatic lenses using resources available to him\, includi
 ng simple algebra\, well-known experimental methods\, and (most significan
 tly) carefully made prisms. Our efforts to clarify his analysis also highl
 ight the need to address a seemingly simple question: what does 'achromati
 c' mean?
LOCATION:Hopkinson Lecture Theatre\, New Museums Site
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