Archived posting to the Leica Users Group, 2001/07/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 02:27 PM 7/27/01 +0200, Mxsmanic wrote: >Leica and most other manufacturers of good lenses use special glasses to obtain >the optical characteristics they require. At one time, Leica had its own glass >lab, and at least one of the glasses it produced contained thorium oxide. >Thorium is a mildly radioactive metal similar to uranium in its radioactivity. >The use of thorium and lanthanum oxides made it possible to obtain very high >indices of refraction with low dispersion, which is useful for correction of >many aberrations. The affected lenses were pre-production and very early production 2/5cm collapsible Summicrons. See Dr Blood's article in VIEWFINDER four or five years back. Leica did, and still does, to my knowledge, have a laboratory for optical glasses, but it has never made its own glass. Until 1926, it used glass from CP Goerz in Berlin and then, after the Zeiss Ikon merger closed that facility, shifted to Schott glass, first from Jena and, after the Second World War, from Mainz. In recent years, some of the Schott glasses supplied have come from Hoya, who manufactures them under license. Marc msmall@roanoke.infi.net FAX: +540/343-7315 Cha robh bąs fir gun ghrąs fir!