Quote Originally Posted by Marco B View Post
Hi all,

I don't own one, nor would have a camera to match it, but I have read before here on APUG about the ultra fast Kodak Ektar Aero 2.5 lenses for aerial camera's dating back to WWII, and I know that some of you probably own one.

In recent times they seem to have gotten a bit of "cult" status due to their nice bokeh when used as portrait lens.

However, there is the question of the radioactivity of the Thorium containing lens elements, and this is the reason for this post.

In last month's edition of the Dutch photo magazine "Camera Magazine", there is an article by Stefan Heijendael, who, after seeing a intriguing advertisement for a 2.5 lens for 4x5 photography, decided to buy one.

Of course, as a good father of two kids, knowing the lens was radioactive didn't chear up himself and his family. He therefore created a do-it-yourself lead covered storage box, but of course as with all matters related to the invisible phenomenon of "radioactivity", the small nagging question kept crawling in the back of his head "Is this enough, and do I actually need to worry at all??"

So he contacted the University of Maastricht here in the Netherlands, where the medical department was willing to help.

So here it is: some real measurements of the level of radiation emitted by such a lens. Better know what you have stored in your seller! :

- At 10 cm from the back of the lens (it's the back lens element containing the Thorium additions), they measured 1.3 microsievert / hour

- At an weekly exposure of 4 hours year-round, this sums up to 270 microsievert in one year.

- The amount of Thorium was estimated to be 36kBQ.

So now the author of course wondered "Is that dangerous?" :o

Our Dutch government uses a maximum of 1000 microsievert / year as an acceptable dosage of radiation to which members of the public may be exposed. The report made up by the medical department therefore concluded that there was "No significant elevated risc", that based on moderate 4 hours weekly usage.

Now on another note, according to this link:

http://encyclopedia.farlex.com/Microsievert

"Humans can absorb up to 0.25 Sv without immediate ill effects; 1 Sv may produce radiation sickness; and more than 8 Sv causes death."

Well, since 1 Sv is 1000 times the accepted year dosis of 1000 microSv, I guess death of owning a Ektar Aero is really not imminent...

Remained just one question by the author Stefan Heijendael, was his lead box completely senseless? Answer: No, 1 mm of lead reduces exposure by a factor of about 20, so if the lens is stored in such a box at more than 1 meter of a subject and with long time exposure, there are no significant riscs from having the lens around in your house...

Well, lastly, since Stefan included it as well, here's the disclaimer :

The department of radiology of the University of Maastricht, the author (Stephan) and I guess myself , do not take any responsibility for negative health effects of owning, storing and using such an Ektar Aero lens. No rights can be obtained based on the measurements. The measurements are based on just a single specimen of this type of lens, and radiation levels may vary...
All of you who own Aero Ektars (and/or Apo Lanthars) and are concerned. Ship your lenses to me and I will safely dispose of them.