[Leica] OT: Fixing radioactive lenses

[geebee at geebeephoto.com (geebee)]

From: "Leonard Taupier" <len-1@comcast.net>

Subject: [Leica] OT: Fixing radioactive lenses


>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
> 
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One man's remedy for the yellowing. May be a little extreme for your 
purposes :-)
http://www.hermes.net.au/bayling/repair.html