[LargeFormat] radioactive lenses

[Clive Warren]

At 3:35 pm -0800 21/11/01, Les Newcomer wrote:
>there was a thread on the graflex helpboard about this and the best
>information was this link
>
>http://people.smu.edu/rmonagha/mf/radioactive.html

Thanks for the URL Les.  Have read through the information there and 
was surprised by the potential levels of radiation from the Aero 
Ektars!

To summarise, Thorium emits Alpha particles. The resulting "daughter" 
products of the radioactive decay of Thorium produces both alpha and 
beta particles. It seems that the decay process of Thorium results in 
the glass becoming progressively more radioactive over time, as the 
more highly radioactive decay products build up in the glass. 
Eventually a more highly radioactive equilibrium will be reached. So, 
over the years when you are expecting the lens to become less 
radioactive they are actually becoming hotter -  more radioactive 
rather than less!

I guess that the radiation is not that harmful, however also found 
the following:

'.....Aero Ektar that is very impressive in girth and weight. One of 
the elements in the rear group is yellow/brown in color and will peg 
the meter on a geiger counter, if placed within 6"'

Hmmmmm..... better keep mine away from stored film then......

Richard Knoppow stated he had read 'suggestions that the color 
correction of the (Aero Ektars) is optimised toward the red since 
aerial cameras are nearly always used with yellow filters and often 
used with IR material. If this is true the lens might exhibit some 
blue fringing'.

The coverage of the 7" lens is 4 1/4 x 4 1/4.

Cheers,
        Clive