Thanks Mark !
...Wayne
-----Original Message-----
From: olympus
[mailto:olympus-bounces+wayne.harridge=structuregraphs.com@xxxxxxxxxxxxxxxxx
] On Behalf Of Mark Marr-Lyon
Sent: Sunday, 20 November 2016 12:05 PM
To: Olympus Camera Discussion <olympus@xxxxxxxxxxxxxxxxx>
Subject: Re: [OM] OM 55/1.2
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 ?
>
> ...Wayne
>
>
>
> -----Original Message-----
> From: olympus
> [mailto:olympus-bounces+wayne.harridge=structuregraphs.com@
> thomasclausen.net
> ] On Behalf Of Mark Marr-Lyon
> Sent: Sunday, 20 November 2016 1:54 AM
> To: Olympus Camera Discussion <olympus@xxxxxxxxxxxxxxxxx>
> Subject: Re: [OM] OM 55/1.2
>
> Thorium (not lanthanum) has a half life comparable to the age of the
> universe, so they'll be radioactive for quite a while yet.
>
> Mark
>
> On Fri, Nov 18, 2016 at 4:04 PM, Wayne Harridge <
> wayne.harridge@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > What's the half-life of the active chemical elements in the lens ?
> > Could be that those old 55/1.2 lenses are now radioactively "dead"
> > by now.
> >
> > ...Wayne
> >
> >
> > -----Original Message-----
> > From: olympus
> > [mailto:olympus-bounces+wayne.harridge=structuregraphs.com@
> > thomasclausen.net
> > ] On Behalf Of Ken Norton
> > Sent: Saturday, 19 November 2016 3:39 AM
> > To: Olympus Camera Discussion <olympus@xxxxxxxxxxxxxxxxx>
> > Subject: Re: [OM] OM 55/1.2
> >
> > > Those with lanthanum glass (e.g. yellowing) are probably optically
> > sharper/better than those without, since generally the lanthanum
> > type glass was used because it had better optical properties
> > (similar to how leaded glass is/was better, despite falling out of
> > favor for various
> reasons).
> >
> >
> > Like killing its owners?
> >
> > AG
> > --
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