If they just had lanthanum in them, they wouldn't be very radioactive at
all. Here's a pretty good summary:
http://camerapedia.wikia.com/wiki/Radioactive_lenses
It's been a while since I looked, but I'm pretty sure the yellowing is a
volume effect on single elements, not an interface effect on the cement of
multiple elements in a group. If anyone really cares, I can try to dig out
the pieces of my radioactive 50/1.4 sometime.
Mark
On Mon, Nov 21, 2016 at 8:14 AM, Sawyer, Edward <Ed.Sawyer@xxxxxxx> wrote:
> I don’t think it’s quite this cut and dried. By the time the OM 55/1.2 and
> others of that vintage came out, they had switched to lanthanum glass,
> rather than Thorium, I believe. Most of the thoriated lenses would have
> been
> late 1940s vintage (Aero Ektars, etc.).
>
> And, the yellowing also can be (or is caused by) a result of interaction
> of the glass and the cement used to hold it together, rather than the glass
> itself yellowing.
>
> -Ed
>
>
> On 11/20/16, 6:16 AM, "olympus on behalf of olympus-request@thomasclausen.
> net" <olympus-bounces+ed.sawyer=unh.edu@xxxxxxxxxxxxxxxxx on behalf of
> olympus-request@xxxxxxxxxxxxxxxxx> wrote:
>
>
> Yes. The yellowing radioactive lenses all used thorium dioxide in them.
> This was replaced by lanthanum oxide, since it's much less radioactive
> which is better for the people who make the lenses as well as not
> yellowing
> over time. Natural lanthanum is slightly radioactive because it has a
> small
> amount of a naturally occurring isotope, but is much less so than
> thorium
> which has no stable isotopes.
>
> Mark
>
> On Sat, Nov 19, 2016 at 5:34 PM, Wayne Harridge <
> wayne.harridge@xxxxxxxxxxxxxxxxxxx> wrote:
>
> >Yes, but is it Thorium in the 55/1.2 ?
>
> --
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