Archived posting to the Leica Users Group, 2010/09/28
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Yes, the Lanthanum-139 used in the elements was often tainted with Thorium. The Thorium alpha's are responsible for knocking electrons out causing the color shift. This can be corrected with UV C btw. I would postulate that the reason this is noticeable in the earlier lenses is due to the coating. The later purple coatings would cover-up any slight yellow tint. Also the Thorium contamination would by nature be very variable and I would assume refining techniques improved as well. Chris At 06:54 AM 9/25/2010, you 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 Chris Saganich MS, CPH Senior Physicist, Office of Health Physics Weill Medical College of Cornell University New York Presbyterian Hospital chs2018 at med.cornell.edu http://intranet.med.cornell.edu/research/health_phys/ Ph. 212.746.6964 Fax. 212.746.4800 Office A-0049