Archived posting to the Leica Users Group, 2007/11/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Ah yes UV A, electron absorption. I suppose a replacement of the electrons kicked out by the thorium or perhaps some atomic level annealing. Either way its better then heating up the lens to 650 degrees in the oven. Chris At 11:21 AM 11/10/2007, you wrote: >For those of you interested in the Pentax 50mm yellowing problem, >Here are photos taken before and after 116 hours exposure to UV light >to reverse the yellow cast problem due to the radioactive element >Thorium in one of the lens elements. > >Before photo. Lens has brownish, yellow cast. > ><http://gallery.leica-users.org/v/LeonardT/Pentax/Takumar_50_2.jpg.html> ><http://tinyurl.com/233emd> > >Here is a photo taken after only 116 hours of being exposed to UV >light. The exposure was to 16 hours of sunlight and 100 hours of UV >from a blacklight. > ><http://gallery.leica-users.org/v/LeonardT/Pentax/ Takumar_116hrs.jpg.html> ><http://tinyurl.com/2bx7do> > >I did not expect any improvement this quickly if at all. I'll >probably keep the lens in front of the blacklight for a few days more >to see if there is any further improvement. > >Thanks for your interest. >Len > > > >_______________________________________________ >Leica Users Group. >See http://leica-users.org/mailman/listinfo/lug for more information Chris Saganich, Sr. Physicist Weill Medical College of Cornell University New York Presbyterian Hospital chs2018@med.cornell.edu Ph. 212.746.6964 Fax. 212.746.4800 Office A-0049