Introduction of Thorium Oxide into Super Takumar Lenses

[ramiller500]

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?
_________________
Sincerely,
Bob Miller

[peterqd]

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)
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Peter - Moderator

[ramiller500]

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.
_________________
Sincerely,
Bob Miller

[peterqd]

[ramiller500]

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.
_________________
Sincerely,
Bob Miller

[ramiller500]

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)
_________________
Sincerely,
Bob Miller

[visualopsins]

(I found it! )

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

http://visualopsins.weebly.com/

Cameras: Canon 5Dc, Spotmatics II, F, ESII, Pentax 6x7

Lenses: S-M-C Takumars 17-500mm (18 lenses), S-M-C Macro-Takumars 50 & 100mm, S-M-C Bellows Takumar, Macro-Takumar 50/4 1:1, S-M-C Takumars/6x7 55-200mm (7 lenses), Micro-Nikkor 55/3.5, Nikkor 50/1.8, 135/3.5 & 200/4, Tamron SP 17/3.5 & 90/2.5

[koji]

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
_________________
My Hone Page has 7,260 photos in 393 directories today.
Lenses: http://www.pbase.com/kkawakami/my_lenses
Cameras: http://www.pbase.com/kkawakami/my_cameras

[ramiller500]

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?
_________________
Sincerely,
Bob Miller

[koji]

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.
_________________
My Hone Page has 7,260 photos in 393 directories today.
Lenses: http://www.pbase.com/kkawakami/my_lenses
Cameras: http://www.pbase.com/kkawakami/my_cameras

[blende8]

And is it the same for the smc 55 and the Super 55?
_________________
Best wishes, Wieland
K20D, K-5
Pentax, mysterium quod absconditum fuit ...

[ramiller500]

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".
_________________
Sincerely,
Bob Miller

[koji]

[koji]

[ramiller500]

Koji,

Please see my revised comment above.
_________________
Sincerely,
Bob Miller