Archived posting to the Leica Users Group, 2007/11/07

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Subject: [Leica] OT: Fixing radioactive lenses
From: len-1 at comcast.net (Leonard Taupier)
Date: Wed Nov 7 17:20:48 2007
References: <27347376-1AD0-40B7-B526-32A6572F1A6D@comcast.net> <200711072256.lA7MuoDn068946@server1.waverley.reid.org>

Hi Marc,

Actually it's not important that I remove the faint yellow of this  
lens because it will not affect the b&w photos I plan on taking with  
it. But it's been documented a few times that the yellow cast is  
considerably diminished after about two weeks exposure to sunlight or  
a UV lamp. Actually the lens is a curiosity to me. If the process  
works I've accomplished two things, one prove the fix works and two I  
can take color photos with a supposedly very good lens. Also I'm a  
little leery about taking lenses apart. I'll take apart a car, a TV  
set or a computer, but a lens or a camera, nope.

Regards,
Len



On Nov 7, 2007, at 5:54 PM, Marc James Small wrote:

> At 05:10 PM 11/7/2007, Leonard Taupier 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.
>
> Len
>
> I love you like a brother, but be conscious here.  The yellow cast  
> may well result from decaying coatings.  Disassemble the lens,  
> remove the lens coatings, and then contemplate the result.  If an  
> element is yellow, then, yes, your original thesis may be correct.
>
> It takes thousands of years for radioactive elements to decay.  I  
> am baffled at the thought that the passage of only a few decades  
> can lead to some change in the color of glass elements.  Maybe I am  
> a babe in the woods -- you guys have locked my heels over the years  
> on things ranging from the utility of Tilley hats to the vibrant  
> necessity of US television -- but I just do not see this as change  
> as a reality.
>
> Do we have any nuclear chemists on the List who can add anything to  
> the discussion?  Jerry Lehrer, I realize, will tell us of his  
> experience at the Brooklyn Home For Broken Boys or whatever it is  
> called, back in 1921 <he grins>, but I really would like to know  
> the straight skinny from guys who regularly have worked with  
> thorium or with thorium glasses.
>
> And, Jerry, you STILL owe me those promised serial numbers from  
> your studio Rollei.  <he grins, yet again>
>
> In short:  can Thorium glass really change color in a few decades?   
> We hear this all the time.  But is it real?
>
> Marc
>
>
> msmall@aya.yale.edu
> Cha robh b?s fir gun ghr?s fir!
>
>
>
> _______________________________________________
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Replies: Reply from jhnichols at bellsouth.net (Jim Nichols) ([Leica] OT: Fixing radioactive lenses)
Reply from marcsmall at comcast.net (Marc James Small) ([Leica] OT: Fixing radioactive lenses)
In reply to: Message from len-1 at comcast.net (Leonard Taupier) ([Leica] OT: Fixing radioactive lenses)
Message from marcsmall at comcast.net (Marc James Small) ([Leica] OT: Fixing radioactive lenses)