Archived posting to the Leica Users Group, 2007/11/08

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Subject: [Leica] OT: Fixing radioactive lenses
From: chs2018 at med.cornell.edu (Chris Saganich)
Date: Thu Nov 8 12:09:07 2007
References: <27347376-1AD0-40B7-B526-32A6572F1A6D@comcast.net> <6.2.1.2.2.20071108110103.015e33e0@pop.med.cornell.edu> <2687855D-C773-4DB1-8C53-39461CBE170F@comcast.net>

Well, I'm curious why it even works at all.  In a typical application color 
is removed from glass by annealing or heating the glass at about 800 F for 
a short time and slowly cooling.  The time and temperature are the main 
issues and a  look into glass annealing (ie gemstone and color center 
activation) should shed some light.  Perhaps a slight elevation of 
temperature for 24 hours?

The UV wavelength for A and B are not high enough per se to cause a 
redistribution of electrons in the atomic valence but UV C does have a high 
enough wavelength.  The only problem is that is how the color is activated 
in the first place, by kicking around electrons!  In order to have the 
process reversed the UV and the glass must have broad energy states in 
common to cause enough heat  absorption to weaken the existing bonding 
allowing new lower energy bonds to form eliminating the number of electron 
radicals in the mix.  Since UV C is more likely to ionize and create 
electron radicals minimizing the UV C would seem like an idea.  Anyway UV C 
is filtered by the atmosphere so if leaving the lenses in the sunlight 
works, the UV C isn't the important agent of change.

At 12:14 PM 11/8/2007, you wrote:
>Thanks Chris
>I stopped using the window sill. I've been putting the lens in the
>sun when it's bright, but most of the time I've been using a BLB
>blacklight bulb. It's only UVA. I don't know which wavelength is most
>effective. I could buy a UVB suntan lamp but I won't spend the money.
>If what I'm doing doesn't work I'll just continue to shoot b&w with
>the lens and be very happy.
>
>Len
>
>
>On Nov 8, 2007, at 11:16 AM, Chris Saganich wrote:
>
>>I believe low-E glass coatings suppress infrared, either way those
>>coatings don't do much for UV.  The UV you would need to reverse
>>the coloration would be quite a bit more then found on a
>>windowsill.  About one month continuous 24/7 exposure would do the
>>trick.  Best to get a UV lamp and a tinfoil lined box.
>>
>>
>>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
>>
>>
>>_______________________________________________
>>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

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 



Replies: Reply from jhnichols at bellsouth.net (Jim Nichols) ([Leica] OT: Fixing radioactive lenses)
In reply to: Message from len-1 at comcast.net (Leonard Taupier) ([Leica] OT: Fixing radioactive lenses)
Message from chs2018 at med.cornell.edu (Chris Saganich) ([Leica] OT: Fixing radioactive lenses)
Message from len-1 at comcast.net (Leonard Taupier) ([Leica] OT: Fixing radioactive lenses)