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03-28-2016, 02:32 AM   #1
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Thorium in Takumar/Pentax 105 f/2.4

I know the Takumar versions of the 105 f/2.4 lens contain elements doped in Thorium. Can anybody confirm if the later Pentax versions are the same (please would you quote source or if you tested, rather than hearsay). Thanks.

03-28-2016, 02:53 AM   #2
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So far as I'm aware, no Pentax K-mount lenses contained Thorium glass.

Last edited by MarkJerling; 04-04-2016 at 04:48 PM.
03-28-2016, 10:06 AM   #3
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QuoteOriginally posted by glass Quote
I know the Takumar versions of the 105 f/2.4 lens contain elements doped in Thorium. Can anybody confirm if the later Pentax versions are the same (please would you quote source or if you tested, rather than hearsay). Thanks.
Just the first Super (non SMC) 6x7 Takumar 105/2.4 is in this list:

Radioactive lenses - Camerapedia - Wikia

Phil.
03-28-2016, 05:39 PM - 1 Like   #4
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Besides Takumar lenses, early Asahi Pentax 6x7 right angle finders had a thorium element; it's not very often you come across these ancient pieces of accessory. Later designated Pentax 67 right angle finders do not have any tainted optics.

It is not a reason to get hyperexcited or cautious. You will be struck by radiation several hundred times in a 24 hour period from myriad sources in daily life, much greater than what you may imagine from a tacky Takumar... For curiosity value and a conversation starter by the fire on a cold winter's day with a cup of Twinings, it's just the thing.

04-03-2016, 11:12 PM - 1 Like   #5
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QuoteOriginally posted by MarkJerling Quote
No Pentax K-mount lenses contained Thorium glass.
Bullshit.

I suppose the fact that you can leave an early S/N SMC-K 50mm f/1.4 on an unexposed polariod for 10 mins, come back and you will have an image of the rear element on it is just a freakish anomaly*.


yellowed 5th element from an SMC Takumar 50mm f/1.4 Before treatment with a 355nm ultraviolet laser.

QuoteOriginally posted by Silent Street Quote
It is not a reason to get hyperexcited or cautious. You will be struck by radiation several hundred times in a 24 hour period from myriad sources in daily life, much greater than what you may imagine from a tacky Takumar
Correct, the amount of radiation emitted is minuscule. Unless you kept a Takumar 50mm f/1.4 in your pocket for 30 years** the accumulated exposure would add up and cause an effect, but personally I can think of many more interesting things that can be done with camera lenses.


* and Pentax wasn't the only manufacturer to experience issues with this: certain Canon,Zeiss,Nikon,Voigtlander and Leica RF and SLR lenses have used glass tainted with radioactive thorium.
**The early Kodak Aero Ektars with lanthanum glass in them are famous for being viciously radioactive, even though they have been around for nearly 100 years: I still wouldn't touch one with a 50 foot pole.

Last edited by Digitalis; 04-03-2016 at 11:34 PM.
04-04-2016, 02:09 PM   #6
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QuoteOriginally posted by Digitalis Quote
Bullshit.

I suppose the fact that you can leave an early S/N SMC-K 50mm f/1.4 on an unexposed polariod for 10 mins, come back and you will have an image of the rear element on it is just a freakish anomaly*.


yellowed 5th element from an SMC Takumar 50mm f/1.4 Before treatment with a 355nm ultraviolet laser.



Correct, the amount of radiation emitted is minuscule. Unless you kept a Takumar 50mm f/1.4 in your pocket for 30 years** the accumulated exposure would add up and cause an effect, but personally I can think of many more interesting things that can be done with camera lenses.


* and Pentax wasn't the only manufacturer to experience issues with this: certain Canon,Zeiss,Nikon,Voigtlander and Leica RF and SLR lenses have used glass tainted with radioactive thorium.
**The early Kodak Aero Ektars with lanthanum glass in them are famous for being viciously radioactive, even though they have been around for nearly 100 years: I still wouldn't touch one with a 50 foot pole.
I have yet to find a Pentax branded K-mount lens with a Thorium element. I can find no evidence, in any lens database, of a Pentax branded K-mount lens with a Thorium element. A SMC Takumar 50mm lens is not a Pentax branded lens, so far as I'm aware.
04-04-2016, 02:53 PM   #7
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QuoteOriginally posted by MarkJerling Quote
I have yet to find a Pentax branded K-mount lens with a Thorium element. I can find no evidence, in any lens database, of a Pentax branded K-mount lens with a Thorium element. A SMC Takumar 50mm lens is not a Pentax branded lens, so far as I'm aware.
The SMC Takumr 50/1.4 is reported to have radioactive element(s). It immediately preceded the SMC Pentax (K-mount) version, and is reported to be essentially the same lens as the K version. It is possible Pentax had a residual supply of thoriated 5th elements in parts inventory when they converted from M42 to K-mount - on Friday they made screw mount, on Monday they made bayonet - thus the observation that an early' SMC Pentax 50/1.4 (K50/1.4) can fog Polaroid film.
04-04-2016, 02:56 PM   #8
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QuoteOriginally posted by MarkJerling Quote
I have yet to find a Pentax branded K-mount lens with a Thorium element. I can find no evidence, in any lens database, of a Pentax branded K-mount lens with a Thorium element. A SMC Takumar 50mm lens is not a Pentax branded lens, so far as I'm aware.
i would read this Radioactive lenses - Camerapedia - Wikia.

Thoriated Camera Lens (ca. 1970s)

There is many more links available.

In the 40 to late 60, thorium oxide glass was commonly use instead of fluorite because it have same properties as fluorite, but much cheaper to produce and use.

Most of the fastest lens of this era used it (most of the fast Taks / the Canon 55/1.2 / Oly's etc ).

04-04-2016, 04:09 PM   #9
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This topic has been discussed at length. See, for instance:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/184271-taku...n-anxiety.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/63093-your-...dioactive.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/119780-taku...dioactive.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/300102-asah...dioactive.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/12182-so-wh...ve-lens-2.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/37246-some-...dioactive.html

As noted prior, I've yet to find an actual Pentax branded K-mount lens with a Thorium element. While it's possible that the factory made one thing on the Friday and another on a Monday, there's no data to support that. And, it's certainly possible that a Pentax branded lens may be found with a Thorium element - but I don't know of anyone who has one.
04-04-2016, 04:15 PM   #10
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QuoteOriginally posted by MarkJerling Quote
I've yet to find an actual Pentax branded K-mount lens with a Thorium element.
I have found several, all 50mm f/1.4 lenses all with low serial numbers, and the characteristic yellowing that comes with glass tainted with radioactive thorium. I didn't buy any of them as I have enough 50mm lenses as things stand. Just because you haven't found one doesn't mean it doesn't exist at all.

QuoteOriginally posted by MarkJerling Quote
A SMC Takumar 50mm lens is not a Pentax branded lens, so far as I'm aware.
Of course: Takumars were all made by Minolta, everyone knows that.

Last edited by Digitalis; 04-04-2016 at 04:32 PM.
04-04-2016, 04:38 PM   #11
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QuoteOriginally posted by Digitalis Quote
I have found several, all 50mm f/1.4 lenses all with low serial numbers, and the characteristic yellowing that comes with glass tainted with radioactive thorium. I didn't buy any of them as I have enough 50mm lenses as things stand. Just because you haven't found one doesn't mean it doesn't exist at all.
Of course, Takumars were all made by Minolta, everyone knows that.
I did not say it does not exist. I have said that the lens databases do not show Pentax branded K-mount lenses that are radioactve and my own tests have not found radioactivity in any Pentax branded lens I have tested. Yellowing of the glass is not a reliable way of testing for radiation as many factors contribute to yellowing of lenses, most notably some of the older glues used in vintage lenses. Sarcasm has no place in this discussion.
04-04-2016, 04:49 PM   #12
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QuoteOriginally posted by MarkJerling Quote
Yellowing of the glass is not a reliable way of testing for radiation as many factors contribute to yellowing of lenses, most notably some of the older glues used in vintage lenses.
True, however when the yellowing is confined to the rear cell of a lens, with the front cell being perfectly clear; it is apparent that something is rotten in the state of denmark.
04-05-2016, 11:15 AM   #13
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QuoteOriginally posted by aurele Quote
thorium oxide glass was commonly use instead of fluorite because it have same properties as fluorite
Don't always believe what you read. Thorium glass is high refractive index, high density, moderately low dispersion. Fluorite is low refractive index, low density and very low dispersion. They were not interchangeable in design.
04-05-2016, 07:11 PM   #14
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QuoteOriginally posted by desertscape Quote
Fluorite is low refractive index, low density and very low dispersion.
And physically, it is a rather soft material. I recall one of the reasons why ISS Astronauts use Nikon cameras and lenses is due to the fact that Flourite in Canon L lenses simply can't handle the vibration and G forces from being launched on a rocket.
04-12-2016, 06:57 AM   #15
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QuoteOriginally posted by gofour3 Quote
Just the first Super (non SMC) 6x7 Takumar 105/2.4 is in this list:

Radioactive lenses - Camerapedia - Wikia

Phil.
I saw this: https://carousell.com/p/42423752

This is the SMC version and seems to have the radioactive element. That list may not be definitive.
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