#1  
Old 12-08-2015, 09:06 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
Pentax Asahi Takumar Radioactive Lens

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:





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
Reply With Quote
  #2  
Old 12-08-2015, 10:57 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,666
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.
Reply With Quote
  #3  
Old 13-08-2015, 05:53 AM
pixelsaurus's Avatar
pixelsaurus (Mike)
Registered User

pixelsaurus is offline
 
Join Date: Mar 2006
Location: Te Kuiti,NZ
Posts: 166
I believe radioactive compounds are no longer used in optical glass manufacture. The EU and other bodies have outlawed as environmentally hazardous.
Reply With Quote
  #4  
Old 13-08-2015, 06:11 AM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
Quote:
Originally Posted by pixelsaurus View Post
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
Reply With Quote
  #5  
Old 13-08-2015, 06:12 AM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
Quote:
Originally Posted by Peter Ward View Post
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
Reply With Quote
  #6  
Old 13-08-2015, 11:32 AM
Retrograde's Avatar
Retrograde (Pete)
a.k.a. @AstroscapePete

Retrograde is offline
 
Join Date: Oct 2011
Location: Sydney
Posts: 1,019
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).

Last edited by Retrograde; 13-08-2015 at 11:52 AM. Reason: clarity
Reply With Quote
  #7  
Old 13-08-2015, 02:07 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,472
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.
Reply With Quote
  #8  
Old 13-08-2015, 02:56 PM
alocky's Avatar
alocky (Andrew lockwood)
PI popular people's front

alocky is offline
 
Join Date: Aug 2010
Location: perth australia
Posts: 1,287
Quote:
Originally Posted by gregbradley View Post
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.
Reply With Quote
  #9  
Old 13-08-2015, 06:15 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
Here's an interesting link:

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

Quote:
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.
Reply With Quote
  #10  
Old 13-08-2015, 06:23 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
And here is a whole list of radioactive lenses:

http://camerapedia.wikia.com/wiki/Radioactive_lenses
Reply With Quote
  #11  
Old 19-08-2015, 06:44 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
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
Reply With Quote
  #12  
Old 24-08-2015, 08:42 AM
sil's Avatar
sil (Steve)
Not even a speck of dust

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,402
Quote:
Originally Posted by alpal View Post
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.
Reply With Quote
  #13  
Old 24-08-2015, 12:22 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
Quote:
Originally Posted by sil View Post
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
Reply With Quote
  #14  
Old 24-08-2015, 07:43 PM
alpal's Avatar
alpal
Registered User

alpal is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 2,834
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
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 01:35 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
OzScopes Authorised Dealer
Advertisement
NexDome Observatories
Advertisement
Meade Australia
Advertisement
Celestron Australia
Advertisement
Bintel
Advertisement
SkyWatcher Australia
Advertisement
Astronomy and Electronics Centre
Advertisement