Archived posting to the Leica Users Group, 2007/11/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks Henning. It's been in front of the black light about 12 hours a day. I'll try it in the back yard on the sunny days. Hopefully it won't attract low flying birds. Len On Nov 7, 2007, at 6:03 PM, Henning Wulff 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. >> >> The fix for removing the yellow cast to the lens is to expose it >> to a UV source like sunlight or a UV light for a week or more. I >> have been putting the lens in a window during the day and exposed >> to a black light at night. >> >> My question is concerning the glass used in my windows. They are >> made of high E glass and have an air space between the double >> panes. I know high E glass is supposed to suppress Infra Red but >> I see no info on if it passes Ultra Violet which is at the >> opposite end of the light spectrum. Does anybody know? >> >> Thanks, >> Len >> >> > > Most glass is quite poor at UV transmission. Just try getting a tan > through a window! > > A black light (flourescent tube type; the incandescents put out > very little UV) is ususally better than putting the lens in the sun > behind glass. If you can put it out in the sun without glass in > front of it, that would be best. > > -- > * Henning J. Wulff > /|\ Wulff Photography & Design > /###\ mailto:henningw@archiphoto.com > |[ ]| http://www.archiphoto.com > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information