Archived posting to the Leica Users Group, 2010/09/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]This is what I had thought and referred to when I used rare-earth, but I was unaware that the 2nd generation Summicrons used Lanthanum elements. The Thorium glass Summicrons are the ones that interest me. Phil Forrest On Sat, 25 Sep 2010 06:54:49 -0400 "Seth Rosner" <sethrosner at nycap.rr.com> wrote: > Phil & others, > > > > I believe you are confusing two different things. Some of the early 50 > Summicrons ( they were all collapsible) were manufactured with glass > one of whose metallic 'rare earth' elements was thorium. It was this > rare earth that resulted in the yellowish tint and the slight > radioactivity emitted by a number of the elements. Leitz recomputed, > more accurately re-designed the 50 Summicron, i.e. the 1956 DR/Rigid > Summicrons, with what they described as thorium-free glass. These > lenses had glass elements with the 'rare-earth', lanthanum, described > in the literature as LaK9 glass. A reason I occasionally used to sign > off on an LHSA communication: LaK9 = Love and Kisses 9 times. ;-) > > > > Seth > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information