[LargeFormat] Van Ripper didn,t know

[Michael Briggs]

On 28-Feb-2004 animal (simon jessurun) wrote:
> Just to be sure i mailed the M.Briggs article to Mr. van Rippen.
> He was unaware of the radioactivity of an aero ektar!.

Was there a previous discussion that I missed?  Do you mean the article by
Frank Van Riper at http://www.washingtonpost.com/wp-srv/photo/essays/vanRiper/
on David Burnett's use of an Aero Ektar.  David Burnett wrote an article at
http://www.digitaljournalist.org/issue0402/dis_burnett.html

> Is there any more quantified info available that you know of on these
> lenses?

There are two articles in 1987 in the British Journal of Photography with
tables of count rates.  Count rates aren't the whole story.

Probaby most photographers, even ones interested in older lenses, are unaware
of how many lenses were made with thorium glass.  Probably almost every major
lens manufacture used this glass for some lens.  Kodak, Leitz, Canon, Nikon,
Pentax and Schneider made some non-military lenses with thorium glass. 
Probably the most common radioactive lens is a particular Pentax, a screw mount
50 mm f1.4 Super-Takumar.   This lens is about as radioactive (according to a
Geiger counter) as the much larger Aero-Ektar!

Lenses aren't the only item in the civilian market that is radioactive.  I was
surprised by the radiation level from the (no longer made) orange Fiesta Ware. 
This is from uranium oxide used in the glaze.

> The reason is that i,m allready exposed to cosmic radiation and would like
> to establish some sort of dosage received.

It is no simple matter to compare the radiation from thorium to cosmic rays.
One has to consider the types of particles, their energies, and their differing
biological effects.  For a camera lens with thorium, either you have to measure
the emitted spectrum, or calculate the amount of shielding done by the lens.
Most radiation safety measurements are done with a geiger counter (count rates),
which doesn't distinguish between types of high energy radiation nor energy,
above its threshold.

> Where would one go to have this tested?

Perhaps someone at a local university will be interested.  Since the
Aero-Ektars were all mass produced, they should all be the same.  If you want a
geiger counter reading, I could locate one in my notes or remeasure.

Most major universities and major corporations that use radiation (radioactive
materials or non-medical x-ray machines) will probably have a person or office
responsible for safety.   The area of physics and these people/offices used to
be called Radiation Safety, but the term Health Physics is more common now. 
Another possibility is the government agency in your country in charge of
radiation safety.

If you want to do some back of the envelope calculations, the highest thorium
content in optical glass that I know of is 28% ThO2 by weight.  Most has less
than this.  You could estimate the thorium content.   By now, all of these
lenses have thorium in equilibrium with its daughters.   Generally the alpha
particles won't reach you because of shielding.  Estimating the entire spectrum
is non-trivial, particuarly when shielding is included.

An even simpler approach would be to use a geiger counter and see at what
distance the lens is undetectable above the background radiation level.  The
inverse square law makes a big effect!

> best regards
> simon jessurun
> amsterdam