Pentax Asahi Takumar Radioactive Lens

[alpal]

I wondered about dark frames taken for astro imaging &
where those rays really came from -
were they cosmic rays or background radiation but then I found out that
some camera lenses are radioactive - in this case Thorium is the culprit used in the glass.
There is a good video about it on Youtube:

Click here to load the video

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I wonder how many other manufacturers use radioactive glass?
Could it be on some coma correctors?
It can't be good for your delicate CCD sensor &
would cause all sorts of annoying streaks in the dark frames & the light frames
basically corrupting your data.

Does anyone know?

cheers
Allan

[Peter Ward]

Holy mole' ! I have one of those lenses ( very sharp by the way)

I used it with a ST10 a while back....but must admit didn't notice anything odd...eg akin to fogging photographic film.

[pixelsaurus (Mike)]

I believe radioactive compounds are no longer used in optical glass manufacture. The EU and other bodies have outlawed as environmentally hazardous.

[alpal]

Originally Posted by pixelsaurus

I believe radioactive compounds are no longer used in optical glass manufacture. The EU and other bodies have outlawed as environmentally hazardous.

Hi Mike,
I hope so.
You'd have to keep a lens like that in a lead box.

cheers
Allan

[alpal]

Originally Posted by Peter Ward

Holy mole' ! I have one of those lenses ( very sharp by the way)

I used it with a ST10 a while back....but must admit didn't notice anything odd...eg akin to fogging photographic film.

Hi Peter,
It would be interesting to see a comparison from your
camera detector with & without the lens in front of it.

cheers
Allan

[Retrograde (Pete)]

I looked into buying one of the Pentax 6x7 Thorium lenses (the 105mm f2.4 I think).
The old Thorium lenses can often be identified by the yellowish appearance of the glass I believe. I decided against it as I thought the yellowing probably wouldn't be ideal for image quality and would only increase with age (one of the examples I saw on ebay showed a significant yellow appearance of the glass). I doubt the radiation given off is significant enough to be any sort of health worry (unless you store it underneath your mattress or something).

[gregbradley]

The yellowing can be reversed by exposure to UV. Leave it out in the sun for a few weeks and it may reverse.

The radiation emitted is light and only a problem if you were using it as an eyepiece although that video would suggest its pretty radioactive.. Having said that there is no definitive research on what a minimum amount of radiation is for no physical effects only what is considered safe. No guarantee. You can google this and come up with a list of lenses that used it. Typically they were fast lenses as the thorium is like fluorite and allows better correction.
They are usually Pentax lenses and a couple of Minolta Rokkor lenses - the 56 F1.2 for example.

I wonder how these Lanthanum eyepieces and lenses would go if tested.

Greg.

[alocky (Andrew lockwood)]

Originally Posted by gregbradley

The yellowing can be reversed by exposure to UV. Leave it out in the sun for a few weeks and it may reverse.

The radiation emitted is light and only a problem if you were using it as an eyepiece although that video would suggest its pretty radioactive.. Having said that there is no definitive research on what a minimum amount of radiation is for no physical effects only what is considered safe. No guarantee. You can google this and come up with a list of lenses that used it. Typically they were fast lenses as the thorium is like fluorite and allows better correction.
They are usually Pentax lenses and a couple of Minolta Rokkor lenses - the 56 F1.2 for example.

I wonder how these Lanthanum eyepieces and lenses would go if tested.

Greg.

Hi Gregg the thorium decay chain actually releases alpha and beta radiation, although you are quite correct in stating that the exposure risk is minimal.
Cheers,
Andrew.

[alpal]

Here's an interesting link:

http://www.bnphoto.org/bnphoto/LostS...adioactive.htm

Radioactive Elements in Glass
Thorium is derived commercially from certain monazite sands (e.g., from India). Thorium is
radioactive itself, emitting alpha particles. The resulting "daughter" products of that radioactive
decay series also produce both alpha and beta particles. Related rare earth such as lanthanum are
often produced from the same sources, with monazite being up to 25% lanthanum.
This decay process means these thoriated glass lenses can gradually become more radioactive over
time, as the more highly radioactive decay products build up in the glass. This result is counterintuitive.
You would expect the radioactivity to decrease over time. But after chemically purifying
the thorium from its ore sources, the thorium is relatively free of these daughter products. Over
time, the thorium decays, and the levels of radioactive daughter by-products builds up. Eventually
a more highly radioactive equilibrium will be reached, as in the original radioactive ores. So over
the years, your "hot" lenses are likely to get more radioactive rather than less. Surprise!

Therefore - the older the lens is the worse it gets.

[alpal]

And here is a whole list of radioactive lenses:

http://camerapedia.wikia.com/wiki/Radioactive_lenses

[alpal]

Update -
I got so interested in this topic that I bought
a sensitive Geiger counter as good as the one in the video.
It's this one here:
http://www.geigercounters.com/PRM-9000.htm

It has the same size pancake Geiger tube as the Inspector EXP seen in the video here:
http://www.geigercounters.com/EXP2.htm

I'll now be able to test all lenses & eyepieces - many other things too.
I should get it in about a week.

Radioactivity can even be found in old green glass items:
https://www.youtube.com/watch?v=OTxZ0aMxW6g


cheers
Allan

[sil (Steve)]

Originally Posted by alpal

Hi Mike,
I hope so.
You'd have to keep a lens like that in a lead box.

cheers
Allan

Over reaction. These are old lenses, been around for decades, have NEVER been linked to any sort of problems by photographers. Use them myself and tested with geiger counters, no appreciable count increase. Calm down.

[alpal]

Originally Posted by sil

Over reaction. These are old lenses, been around for decades, have NEVER been linked to any sort of problems by photographers. Use them myself and tested with geiger counters, no appreciable count increase. Calm down.

OK - so nothing like the one I posted in the video?

By the way my Geiger counter arrived this morning.
I am just checking background levels which are normal to below normal.
I haven't got a lens to test yet.

cheers
Allan

[alpal]

Update:

I got the PRM-9000 today & it has been fascinating.
I don't have any old camera lenses to test but there are other objects.

I took some measurements of 2 types of Lead/Tin solder &
also a crystal vase which was the most radioactive I could find at my place.
I checked these against the background.
CPM = counts per minute.
The results are here:


Background 0.090uSv/hr 20 minute sample
background 28 CPM 5 minute sample

Solder Type A 0.230 uSv/hr 20 minute sample
Solder Type A 74 CPM 5 minute sample

Crystal vase 0.330 uSv/hr 5 minute sample
Crystal vase 121 CPM 5 minute sample

Solder Type B 0.130 uSv/hr 5 minute sample
Solder type B 53 CPM 5 minute sample


What do you all think?
As far as I can tell:
There is nothing there that is very radioactive but still I have found results above the background level from normal objects.
I would bet that all the results are caused by Pb 210.

cheers
Allan