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Introduction of Thorium Oxide into Super Takumar Lenses
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PostPosted: Wed Jan 12, 2011 3:49 pm    Post subject: Introduction of Thorium Oxide into Super Takumar Lenses Reply with quote
I would like to pinpoint the calendar year (or at least the approximate serial number) in which a lens element containing thorium oxide was first used in any Super Takumar normal lens. What is really known about this?


PostPosted: Wed Jan 12, 2011 4:23 pm    Post subject: Reply with quote
Thoriated Takumars are :
- Super Takumar 35/2 (V2, 49mm filter) introduced 1968
- S-M-C Takumar 35/2 1972
- Super Takumar 50/1.4 (V2) 1967
- S-M-C Takumar 50/1.4 1971
- Super and S-M-C Takumar 6X7 105/2.4 1969 (I think)


PostPosted: Wed Jan 12, 2011 4:58 pm    Post subject: Reply with quote
I've seen Web claims that at least one 55mm/2 Super Takumar lens was not radioactive whereas some other 55mm/2 and 55/1.8 (same design) Super Takumar lenses were radioactive. Unfortunately, the claims did not reference the serial numbers or years of manufacture of the lenses tested.

I've also seen claims that some 50mm/1.4 Super Takumars of the 8-element design were not radioactive whereas others of this design were.


PostPosted: Wed Jan 12, 2011 6:54 pm    Post subject: Reply with quote
ramiller500 wrote:
I've seen Web claims that at least one 55mm/2 Super Takumar lens was not radioactive whereas some other 55mm/2 and 55/1.8 (same design) Super Takumar lenses were radioactive. Unfortunately, the claims did not reference the serial numbers or years of manufacture of the lenses tested.

I've also seen claims that some 50mm/1.4 Super Takumars of the 8-element design were not radioactive whereas others of this design were.

There seems to be some doubt about the 2/ & 1.8/55s. I have both in Super-Tak and neither are thoriated. I think this design existed for the whole time so I doubt whether any were. As for the 8-element 1.4/50, this is version 1 which was definitely not thoriated.

Takumar serial numbers were not consecutive and therefore can't be relied upon for relative dates.


PostPosted: Wed Jan 12, 2011 8:39 pm    Post subject: Reply with quote
We ought to keep in mind that detectable thorium levels lower than those found in the later Super Takumar 50mm/1.4 lenses might not yellow the glass at all.


PostPosted: Mon Jan 17, 2011 2:14 pm    Post subject: Reply with quote
I did some more Web investigation, and it appears that Asahi Optical touted the "rare earth glass" in all their 55mm/1.8 and 55mm/2 Takumar lenses as least back to the Auto-Takumars around 1960. The f/2 lens and f/1.8 lens had the same formula and glass.

[Generally, the f/2 lenses had a waterhouse stop to keep from using them at f/1.8 ! However, I recently obtained a Super Takumar 55mm/2 of the earliest type ("2" at the left of the numbers on aperture ring) that has an unmarked clicked stop that is really f/1.8.]

See http://www.taunusreiter.de/Cameras/Pentax_Takumar_e.html

"Rare earth glass" often contains some thorium oxide.

Just because these 55mm lenses are usually not yellowed does not mean there is no thorium oxide. However, these have been shown to be less radioactive than the Super-Takumar and SMC Takumar50mm/1.4 lenses that typically yellow.

Also, at some point, Asahi Optical may have transitioned from a rare earth glass without thorium to one with thorium.

(revised 19 Jan 2011)

Last edited by ramiller500 on Wed Jan 19, 2011 12:50 pm; edited 1 time in total


PostPosted: Mon Jan 17, 2011 4:41 pm    Post subject: Reply with quote
(I found it! Very Happy)

Robert Monaghan's 'lost' web page "Radioactive Glass in Lenses
Are Your Lenses Really "Hot"?!!"


PostPosted: Mon Jan 17, 2011 6:27 pm    Post subject: Reply with quote
Super Takumar 1.8/55 has "reputation" of radioactiveness. There is one
article by some japanese fellow, here>

http://homepage1.nifty.com/nekocame/camera/atomlens.htm

In the middle of the above page, the table is arranged to left to right:

maker ... lens name ... SN ... front of lens ... back of lens ... back of body ... name of body used

in this order. The unit of values are micro-Sievert per hour of gamma radiation (μSv/h),
and environmental value is around 0.050 ~ 0.060 μSv/h. He measured radioactivity at the front,
back of the lens, and at the back of the camera with the lens mounted.

For your information, you receive 50μSv when you get X-ray in your hospital.

So Super-Takumar has about 100 time higher radioactive gamma radiation than
natural environment has. There is no radioactive 1.8/55 or 2/55 too btw.

note: Super-Takumar 2/55 (M42) or SMC Takumar 2/55 (K mount) were not sold
in japanese market, these are export only versions experts say. Pentax just
pinched lens internal opening to have F2 from 1.8/55 lens, and sold them abroad.

Radiation: http://en.wikipedia.org/wiki/Ionizing_radiation
Radiation poisoning: http://en.wikipedia.org/wiki/Radiation_poisoning


PostPosted: Tue Jan 18, 2011 2:27 pm    Post subject: Reply with quote
Koji, in the table found in your Japanese link, the 1:1:8/55mm lens with serial number 763144 had no numerical readings next to it, unlike the others with higher serial numbers. Does this signify that lens 763144 had no radioactivity above background level?


PostPosted: Tue Jan 18, 2011 3:05 pm    Post subject: Reply with quote
Yes, you got it. The author says cannot detect any gamma radiation among
some of Super Takumar 1,8/55 and 3,5/135s.

note: Pentax's serial numbers are notoriously unrelated to their production chronology. Rolling Eyes

Last edited by koji on Tue Jan 18, 2011 3:09 pm; edited 1 time in total


PostPosted: Tue Jan 18, 2011 3:07 pm    Post subject: Reply with quote
And is it the same for the smc 55 and the Super 55?


PostPosted: Tue Jan 18, 2011 3:09 pm    Post subject: Reply with quote
Koji,

So, among the 1.8/55's, did the serial numbers other than 763144 have a different glass formula?

I'm curious, because I have a 2/55 with a serial number in the 760,000's. This is the very first 2/55 version from ~1962 with a "reversed" aperture ring. It has an unmarked click stop where "1.8" should be, and the aperture even opens up a bit when the ring is moved from 2 to the phantom "1.8".

Last edited by ramiller500 on Wed Jan 19, 2011 8:58 pm; edited 2 times in total


PostPosted: Tue Jan 18, 2011 3:10 pm    Post subject: Reply with quote
blende8 wrote:
And is it the same for the smc 55 and the Super 55?


I want to ask the same question to Pentax specialists. Very Happy
Too many different lens names from Pentax Takumars. Sad


PostPosted: Tue Jan 18, 2011 3:15 pm    Post subject: Reply with quote
ramiller500 wrote:
Koji,

So, among the 1.8/55's, why were numbers and colored shading shown in this Japanese table for the serial numbers other than 763144?


Those colour shadings try to indicate "strength" of radiation among
Takumars I guess. 50/1.4s have 100 times more than background level
whereas 55/1.8s have one third of it.

No explanation from the author, so the above is my guess.


PostPosted: Tue Jan 18, 2011 3:19 pm    Post subject: Reply with quote
Koji,

Please see my revised comment above.


PostPosted: Tue Jan 18, 2011 3:27 pm    Post subject: Reply with quote
My Auto-Takumar 55/1.8, with the reversed aperture ring and otherwise similar to what a Super would be, has absolutely clear glass. My SMC Takumar is also clear, though it of course has the SMC coatings.

Also, I think it's proper to say that the lens bonding glue yellows rather than the glass, due to the radiation.


PostPosted: Tue Jan 18, 2011 4:42 pm    Post subject: Reply with quote
ramiller500 wrote:
Koji,

So, among the 1.8/55's, did the serial numbers other than 763144 have a different glass formula?

I'm curious, because I have a 2/55 with a serial number in the 700,000's. This is the very first 2/55 version from ~1962 with a "reversed" aperture ring. It has an unmarked click stop where "1.8" should be, and the aperture even opens up a bit when the ring is moved from 2 to the phantom "1.8".


Sorry I have no knowledge about Takumar optics nor
their naming of Super, SMC, S-M-C, Super-multi-Coating, etc. etc. Embarassed

All I know is I have Super-Takumar 1.8/55 and SMC Takumar 1.4/50,
Takumar Macro 55/4 and Super-Multi-Coated TAKUMAR 3.5/35 (all M42)
and SMC PENTAX 3.5/28, 2/55, and 3.5/135 (all K mount).

As I said before, want to know those naming difference signifies what? Confused


PostPosted: Wed Jan 19, 2011 12:37 am    Post subject: Reply with quote
Besides referring to coatings, the lens names have historical significance, the order of production. First were preset Asahi Takumar and Auto-Takumar, Super, Super-Multi-Coated, and Pentax SMC, all M42 mount, then Pentax SMC in K-mount. The first is coated with one layer, maybe two, the Super has three layers, the S-M-C and SMC have 7 layers.

A reference web site for Takumar lenses is http://www.aohc.it/

For example: M42x1 Standard Takumar lenses for Asahi Pentax cameras


PostPosted: Fri Dec 09, 2011 4:05 pm    Post subject: Reply with quote
I'd like to resurrect this thread because my Super-Takumar 55/1.8 seems to be very yellow. It's pretty disconcerting... I'll see whether I can find a Geiger counter to check just how serious it is.

EDIT: Embedding does not seem to work, for some reason, so here's the link: http://i212.photobucket.com/albums/cc84/Wosis2/-1-1.jpg


PostPosted: Fri Dec 09, 2011 4:31 pm    Post subject: Reply with quote
noctilux wrote:
I'd like to resurrect this thread because my Super-Takumar 55/1.8 seems to be very yellow. It's pretty disconcerting... I'll see whether I can find a Geiger counter to check just how serious it is.

EDIT: Embedding does not seem to work, for some reason, so here's the link: http://i212.photobucket.com/albums/cc84/Wosis2/-1-1.jpg

That's because it's your first post, it's an anti-spam-mechanism.


PostPosted: Fri Dec 09, 2011 5:30 pm    Post subject: Reply with quote
OMG, will this "radioactive lens" thing ever end - PLEEEZZZE have mercy Smile


PostPosted: Fri Dec 09, 2011 6:16 pm    Post subject: Reply with quote
My S-M-C Takumar 55mm f/1.8 lens is very slightly yellow, but seems to be about 3/4 as radioactive as the 50mm f/1.4 S-M-C Takumar.

Close to the rear element (with rear lenscap off), the reading was about 15000 counts/minute (CPM) measured with a typical thin-window 1.75-inch pancake probe (alpha+beta+gamma). With the plastic cap over the probe, the reading was about 8000CPM. Most gammas and quite a few of the betas should reach the probe with the cap on, but few, if any, alphas would get through. The background count averages about 25-40CPM.

Note that this probe is not very good at picking up gamma, and I have no way to post readings in uSv/hr, since the geiger counter is calibrated for Cs137, not Thorium in secular equilibrium with a long chain of radioactive decay products.

I don't have a YouTube video of this (yet), but here's one of the Super Takumar 55mm f/2: http://www.youtube.com/watch?v=T0h-7iAstlA, and one of the later 55mm f/1.8 SMC Takumar: http://www.youtube.com/watch?v=oL3D7FQTHXo&feature=related


PostPosted: Fri Dec 09, 2011 10:42 pm    Post subject: Reply with quote
noctilux wrote:
I'd like to resurrect this thread because my Super-Takumar 55/1.8 seems to be very yellow. It's pretty disconcerting... I'll see whether I can find a Geiger counter to check just how serious it is.

EDIT: Embedding does not seem to work, for some reason, so here's the link: http://i212.photobucket.com/albums/cc84/Wosis2/-1-1.jpg


The anti-reflective coating has a yellow/gold tint to it's reflection, which is what I see in this picture.


PostPosted: Fri Dec 09, 2011 11:08 pm    Post subject: Reply with quote
peterqd wrote:

There seems to be some doubt about the 2/ & 1.8/55s. I have both in Super-Tak and neither are thoriated. I think this design existed for the whole time so I doubt whether any were.


I have S-M-C 55mm f/1.8 and Super 55mm f/2, both are equally radioactive when measured with a geiger counter. Notably they did not appear anywhere near as yellowed as the S-M-C 55mm f/1.4 did before UV treatment, so I would speculate that many conflicting reports come from people who falsely rely on yellowing as a sign of radioactivity (which it isn't very reliably one way or the other) instead of measuring the lenses.

Last edited by Arkku on Tue Dec 13, 2011 4:25 pm; edited 1 time in total


PostPosted: Tue Dec 13, 2011 10:28 am    Post subject: Reply with quote
Lightshow wrote:

The anti-reflective coating has a yellow/gold tint to it's reflection, which is what I see in this picture.


You're quite right, the lens is actually perfectly clear! Then again, Arkku and some web sites point out that the yellowing is not a necessary consequence of Thorium oxide.

There is a great deal of scoffing going on by lens owners about the radioactivity concerns, and perhaps it is justified. There are some assumptions I find unconvincing, however. Take the comparison with the long distance flight: Sure, one flight may impart a higher dose, but it is generally done only once in a while; a lens is used much more often. Also, there is no dose which is completely harmless -- any ray can potentially destroy a cell's DNA, so any increase in radiation level will increase the amount of DNA destroyed which the body has to repair. Thus, any additional source of radiation poses an additional risk.

Two arguments would be convincing: One would be to show that the increased radiation level is easily handled by the body's repair mechanisms; the second would be to show that in practical use, background radiation levels are not raised significantly (the question whether the background is harmless itself is a separate question).

I do not know about the first, but I'd like to tackle the second:
Alpha particles should be harmless, as they are easily blocked by the camera body at the back, a UV filter at the front and the lens housing at the sides. The last point is quite important, as manual focusing means that one hand is permanently on the lens.
There are two further issues, though: Firstly, Thorium does not decay purely through alpha, but also through gamma decay. Secondly, the decay products of Thorium themselves further decay through beta and gamma decay. Gamma rays in particular are hard to shield and could be an issue.
Let's deal with the first issue first: Alpha decay can happen in two ways. It either decays directly, emitting the full energy; or it decays with a slightly lower energy, producing an excited atom. This excited atom then decays, emitting a gamma ray. In Thorium, the majority of the decays is pure alpha decay (Source), so the amount of gamma radiation should be low.
The second issue -- subsequent decay -- ought to be negligible, for the following reason: The rate of radioactive decay is proportional to the amount of particles that are radioactive. Since Thorium 232 decays very slowly (14*10^9 years half life), its decay products are few and should thus have a low decay rate.

All in all: Thorium should indeed emit mainly alpha radiation which is dangerous only if it is unshielded and closer than about 4cm to the body. If the lens is not inhaled, consumed or snuggled continuously, all should be OK. :)

Last edited by noctilux on Tue Dec 13, 2011 11:51 am; edited 6 times in total
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