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[OM] Re: An interesting item on *bay (radioactive 24/2?)

Subject: [OM] Re: An interesting item on *bay (radioactive 24/2?)
From: Mark Marr-Lyon <markml@xxxxxxx>
Date: Tue, 02 Nov 2004 12:20:22 -0700
Some time ago I measured all the silvernose lenses I have.  Here are the 
results (sorry if the table doesn't look good):

Lens            Serial #        Radioactive?
16/3.5        1010xx        No.
35/2.8        1099xx        Yes. 1300 counts/min from the front, less from back.
50/1.8        1168xx        No.  M-System lens.
55/1.2        1099xx        Yes.    80,000 counts/min from front or back.
75-150/4   1440xx        No.
85/2           1028xx        No.
100/2.8      1268xx        No.
135/2.8      1359xx        No.
300/4.5      1109xx        Yes. 800 counts/min from the back, less from front.

With the early 50/1.4, this makes 4 known radioactive OM Zuikos. Note that both 
the 35/2.8 and 300/4.5 are far less radioactive than the 55/1.2 (or 50/1.4). 
The amount of yellowing in these lenses is much less than that of the 55/1.2, 
if even noticable. For reference, the small calibration source of uranium 238 
attached to the meter read 200,000 counts/minute, and the background reading 
was 100-200 counts/minute.
 
This was using a different meter than the first time I measured.  The higher 
counts with this meter can be attributed to the larger detector area, as well 
as the fact that this meter was sensitive to alpha particles.

So, it's possible the early 24/2's are radioactive too, though I would guess 
that they're at about the same level as the 35/2.8 or 300/4.5, and that the 
yellowing is barely noticable or not at all.  The picture of the lens on e*ay 
that was pointed out wasn't really conclusive for me, since the background is 
yellow anyway, and it could just be shadowed.

Mark

On Monday, November 01, 2004, at 11:54PM, Jeff Keller <jrk_om@xxxxxxxxxxx> 
wrote:
>There were quite a few posts about the early 50mm f1.4 having a radioactive 
>element. I don't remember the ser.no. cut-off. The number 118xxx is what I 
>remember but I could be way off (couldn't find it in the archives).. Mark 
>Marr-Lyon posted some readings indicating the front element was the source. 
>I believe someone else posted some readings but I couldn't find those 
>either.
>-jeff


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