Archived posting to the Leica Users Group, 2001/07/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Marc I imagine that the Schott glasses are ideal for dispensing fine single malts, neh? (hic!) Dan (TGIF) Post - ----- Original Message ----- From: "Marc James Small" <msmall@roanoke.infi.net> To: <leica-users@mejac.palo-alto.ca.us> Sent: Friday, July 27, 2001 10:08 AM Subject: Re: [Leica] Radioactive glass in M lenses ? > 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! > >