Archived posting to the Leica Users Group, 2007/11/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Marc, Actually it's not important that I remove the faint yellow of this lens because it will not affect the b&w photos I plan on taking with it. But it's been documented a few times that the yellow cast is considerably diminished after about two weeks exposure to sunlight or a UV lamp. Actually the lens is a curiosity to me. If the process works I've accomplished two things, one prove the fix works and two I can take color photos with a supposedly very good lens. Also I'm a little leery about taking lenses apart. I'll take apart a car, a TV set or a computer, but a lens or a camera, nope. Regards, Len On Nov 7, 2007, at 5:54 PM, Marc James Small wrote: > At 05:10 PM 11/7/2007, Leonard Taupier wrote: > >I have an old Pentax 50/1.4 Super Takumar that has, over time, > >yellowed due to one of the elements containing Thorium, a mildly > >radioactive element. The addition of thorium makes a very high > >refractive index glass, and a very good lens. This lens is probably > >one of the most famous lenses with this element but I'm sure there > >were more. > > Len > > I love you like a brother, but be conscious here. The yellow cast > may well result from decaying coatings. Disassemble the lens, > remove the lens coatings, and then contemplate the result. If an > element is yellow, then, yes, your original thesis may be correct. > > It takes thousands of years for radioactive elements to decay. I > am baffled at the thought that the passage of only a few decades > can lead to some change in the color of glass elements. Maybe I am > a babe in the woods -- you guys have locked my heels over the years > on things ranging from the utility of Tilley hats to the vibrant > necessity of US television -- but I just do not see this as change > as a reality. > > Do we have any nuclear chemists on the List who can add anything to > the discussion? Jerry Lehrer, I realize, will tell us of his > experience at the Brooklyn Home For Broken Boys or whatever it is > called, back in 1921 <he grins>, but I really would like to know > the straight skinny from guys who regularly have worked with > thorium or with thorium glasses. > > And, Jerry, you STILL owe me those promised serial numbers from > your studio Rollei. <he grins, yet again> > > In short: can Thorium glass really change color in a few decades? > We hear this all the time. But is it real? > > Marc > > > msmall@aya.yale.edu > Cha robh b?s fir gun ghr?s fir! > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information