Archived posting to the Leica Users Group, 2014/02/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]As far as I can find out older lenses that contained lanthanum in order to achieve high refractive indices, contained Thorium Oxide which is mildly radioactive.I do not know if these are the only type involved. For more details see here: http://en.wikipedia.org/wiki/Low_dispersion_glass and here http://camerapedia.wikia.com/wiki/Radioactive_lenses which gives a fairly extensive list and here http://www.orau.org/ptp/collection/consumer%20products/cameralens.htm Peter On 11/02/2014 21:22, Marty Deveney wrote: > There are better, more stable ways to make high refractive index glass. I > think lanthanum was largely discontinued in camera lenses for these > practical reasons rather than anything to do with health. > > Marty > > > On Tuesday, 11 February 2014, Howard Ritter <hlritter at bex.net> wrote: > >> Lanthanum is mildly radioactive, but not so much so that its use in >> eyepieces for astronomical telescopes is prohibited. Several manufacturers >> advertise that their products contain lanthanum glass. >> >> --howard >> >> >> On Feb 11, 2014, at 6:51 AM, Peter Dzwig <pdzwig at >> summaventures.com<javascript:;>> >> wrote: >> >>> Guys, >>> >>> Knowing your expertise.... >>> >>> What is the issue with Lanthanum in lenses. I thought its use had been >>> discontinued long ago on health grounds, maybe in the 50s, although what >> the >>> details were I don't recall. Now someone else tells me otherwise. >>> >>> ...were there other compounds discontinued for similar reasons? >>> >>> Peter >>> -- >>> >>> =========================================================== >>> Dr Peter Dzwig >>> >>> >>> _______________________________________________ >>> Leica Users Group. >>> See http://leica-users.org/mailman/listinfo/lug for more information >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information >> > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > -- =========================================================== Dr Peter Dzwig