Re: Lathanum-lensed eyepieces

From: Richard (rander3127_at_rogers.com)
Date: 07/02/04 

Date: 2 Jul 2004 14:47:02 -0700

Chris L Peterson <clp@alumni.caltech.edu> wrote in message news:<bnj8e0hnpo7gru980r6gl3a64o3aldbjve@4ax.com>...
> On 1 Jul 2004 10:17:37 -0700, rander3127@rogers.com (Richard) wrote:
>
> >Anyone put a geiger counter next to one? :)
> >-Rich
>
> Lanthanum isn't necessarily radioactive. However, does have a radioactive
> isotope that is frequently mixed in, but the decay rate is very low. I doubt you
> could measure any radiation with an ordinary detector.
>
> They used to use thorium in some camera lenses. Their production of radiation
> increased with time, and was high enough to fog film if left on the camera for a
> few years.
>
>

Yes, I read something about the original Pentax SLRs (I had one) having their
50mm lens with a radioactive element in them.
-Rich

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