Archived posting to the Leica Users Group, 2011/04/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]And this magic Ikea ten-dollar lamp did it in twelve hours! >Wow! Time flies. I did a lot of research on Thorium yellowing in >2007 and took these two photos of my Pentax 50mm f1.4 Super Takumar >lens. It took me a total of 116 hours to remove the yellow cast, >exposing the lens to UV at night and sunlight during the day. Here >are the before and after photos. > >http://gallery.leica-users.org/v/LeonardT/Pentax/ > >It was during this timeframe that Jim Nichols investigated his >Pentax lens for yellowing. > >I believe I have a technical paper explaining the phenomena >somewhere. If I find it I'll post it. > >I was not aware that the 90mm Summicron used Thorium. It must be an >early model as leica stopped using Thorium in the crossover period >between the 50mm Summitar and Summicron around 1954. The 90mm >Summicron was introduced in 1957. > >Len > > > >On Apr 20, 2011, at 4:30 PM, Herbert Kanner wrote: > >>Thanks for the kind word, George. Byron Rakitzis suggested that my >>speculation as to the cause of the yellow was probably incorrect, >>and suggested a Google search. I found a lot of information >>indicating that the yellow was due to radiation damage from gamma >>rays emitted by some of the daughter products of the decayed >>thorium. No information as to why a few hours application of UV >>cures this. >> >>Herb >> >> >>>On Apr 19, 2011, at 12:23 PM, Herbert Kanner wrote: >>> >>> > So now I concluded that the balsam was fine, and that this lens >>>had at least one thorium glass element. I headed to Ikea, where I >>>had never been before. I felt like a lab rat in a maze; everyone >>>should have that experience ONCE. By some miracle I found a desk >>>version of that lamp $9.89, assembly required! I applied the >>>recommended twelve hours of exposure, and the yellow is gone gone >>>gone. >>> >>> >>>Kudos! Herbert. >>>and thanks for the detailed and useful information. >>> >>>Regards, >>>George Lottermoser >>>george at imagist.com >>>http://www.imagist.com >>>http://www.imagist.com/blog >>>http://www.linkedin.com/in/imagist >>> >>> >>> >>> >>> >>> >>>_______________________________________________ >>>Leica Users Group. >>>See http://leica-users.org/mailman/listinfo/lug for more information >> >>-- >>Herbert Kanner >>kanner at acm.org >>650-326-8204 >> >>Do not meddle in the affairs of cats, >>for they are subtle and will pee >>on your computer! >> >>_______________________________________________ >>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 -- Herbert Kanner kanner at acm.org 650-326-8204 Do not meddle in the affairs of cats, for they are subtle and will pee on your computer!