[rollei_list] Re: OT 24" Aero Ektar.
- From: Laurence cuffe <cuffe@xxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 05 Jan 2011 17:33:35 +0000
On 3 Jan 2011, at 19:53, Emmanuel Bigler wrote:
David Sadowski a écrit :
Is the radioactivity from exposure during high altitude use, or
were radioactive matetials used to make parts glow in the dark in
the manner of radium watches? Are these lenses from the WWII era?
To the best of my knowledege (I remember that this issue was
discussed here in the past), radio-activity in lens glasses is du to
radio-active materials used on inside the glass. For example
thorium, but NOT lanthanum wich is not at all radio-active.
It has been reported that exposing tea-coloured lens elements to UV
light (same UV sources as used in contact printing photography for
platinum/plalladium of gum bichromated prints) for a very long time
may help "bleaching" the glass.
See this recent report by Jean-baptiste Maison (in French, but the
images speak for themselves) about this procedure... for an aero-
ektar.
http://www.galerie-photo.com/decolorer-aero-ektar.html
After 500 hours, some de-coloration has taken place bu the glas is
still not completely transparent. At least images can be taken with
soem coulour cast.
Regarding the use of radioactive materials in watches, there is
still a demand for instruments illuminated by permanent light
sources based on tritium capsules.
See this Swiss company
http://www.luminox.com/
--
Emmanuel
I got my Geiger counter going again, and tested the lens for radio
activity.
The 24" appears to be significantly more radio active than the 7",
while the 7" registered a very respectable reading of about 300 counts
per second, when I lowered the probe into the back of the 24" Aero
Ektar, the needle pinned at over 2000 counts per second.
I have removed it to the back of the garage.
All the best
Laurence Cuffe
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