[UncleVanya]

Looking at that video, I'm not clear it is an eight element lens. The images of the lens aren't entirely convincing since the rear element isn't displayed in the manner that would help identify it. As someone who had an eBay dispute over a seven element 50 1.4 sold as an eight element... I got pretty familiar with the ways these lenses can be made to appear to be each other.

[stevebrot]

Here is the video of the 8 element testing positive with the Geiger counter.

Thanks for the video. As you might have noted, the Camerapedia wiki entry has been disputed. The level recorded in the video is quite low,* low enough that I suspect it might be due to incidental rare earth contamination in the glass of some samples and/or radiation in the lens body. A thorium-doped lens would have pegged the meter. The proof of the pudding remains the brownish discoloration of hot lenses

Why I'm still skeptical that the 8s are not radioactive is because Pentax won't just come out and say it.

That is pretty silly. The lens was made in the early 1960s and Asahi/Pentax has never made a statement one way or the other regarding thorium doping of any of its lenses. Similarly, the same is true of the makers of other thorium-doped lenses.

I appreciate your health concerns and given such, you might want to simply avoid suspect lenses as you see fit. You might also want to invest in a Geiger counter/dosimeter similar to that used in the video.


Steve

* 1 μSv/hr is painfully low and is on the order of the natural background radiation in many parts of the world.

[Lowell Goudge]

Thanks for the video. As you might have noted, the Camerapedia wiki entry has been disputed. The level recorded in the video is quite low,* low enough that I suspect it might be due to incidental rare earth contamination in the glass of some samples and/or radiation in the lens body. A thorium-doped lens would have pegged the meter. The proof of the pudding remains the brownish discoloration of hot lenses



That is pretty silly. The lens was made in the early 1960s and Asahi/Pentax has never made a statement one way or the other regarding thorium doping of any of its lenses. Similarly, the same is true of the makers of other thorium-doped lenses.

I appreciate your health concerns and given such, you might want to simply avoid suspect lenses as you see fit. You might also want to invest in a Geiger counter/dosimeter similar to that used in the video.


Steve

* 1 μSv/hr is painfully low and is on the order of the natural background radiation in many parts of the world.

but at the end of the day, you are not sleeping with the lens, and the real issue with thorium doped lenses, is for the workers that are prone to inhale/ingest dust. as long as you dont grind the lens up and eat it i don't think there is a risk.

if it was that dangerous, people would be scanning / detecting radio active material being shipped by mail and courier yet we dont hear anyting

[PJ1]

Another way to tell the 8-element from the 7-element is the rear element. That can not be faked.

The lens on the left is a 7 element lens that has been doctored. The red IR mark is directly above the 4 and the white mark would be to the left of it (if the lens was looked at the usual way with the objective uppermost). Someone has painted the white mark red and the red mark white. There is NO Takumar 50/1.4 in which the IR mark is directly above the 4. The supposed "hybrid" is simply a fraud.

[zvon]

Takumar 50mm f1.4 M42 8 elements - radioactive! - YouTube

Here is the video of the 8 element testing positive with the Geiger counter. It was posted a month ago, and this website is now updated when new info regarding the 8 also being radioactive.

Radioactive lenses | Camerapedia | Fandom

It's simply a list of known radioactive and known non radioactive lenses.

Why I'm still skeptical that the 8s are not radioactive is because Pentax won't just come out and say it. That would put all of it to rest. I just want to find a definitive answer before throwing 350 bucks away on a lens I may not even be able to keep in the house. I'm not sure there are any places that offer Geiger service, and with Covid I can't exactly walk up to the fire station and ask them. Not with the whole state of CA on fire here right now.

Who else would offer such a service? And would they be able to test for alpha, as well as the daughter beta and gamma that it releases that are the real threat?

1 micro sievert per hour is not radioactive. That is equivalent to eating 10 bananas in an hour. People are really trying hard to make some sort of a scandal with thorium lens with these types of videos showing all sort of things that are questionable.


I have both 7 and 8 element and 8 element is better in my opinion. I don't like the look of 7 element when wide open.

[stevebrot]

There is NO Takumar 50/1.4 in which the IR mark is directly above the 4. The supposed "hybrid" is simply a fraud.

EXCEPT for the parts-bin-overlap 8-element example on the Takumar Field Guide site shown in comment ABOVE.


Steve

[PJ1]

EXCEPT for the parts-bin-overlap 8-element example on the Takumar Field Guide site shown in comment ABOVE

Don't know about any parts bin but I repeat

There is NO Takumar 50/1.4 in which the IR mark is directly above the 4.

The lens shown is one that has been repainted. Compare it with a 7 element version. The switch of the colours is apparent. And on that note, I have made my last post here.

[stevebrot]

Don't know about any parts bin but I repeat
The lens shown is one that has been repainted. Compare it with a 7 element version. The switch of the colours is apparent. And on that note, I have made my last post here.

Thanks for the last word. As with you, this is my last contribution to this off-topic, but inevitable spur.

The lens shown is an obvious fake* and your repetition is noted. Nobody is suggesting otherwise, but the assertion of "NO" ST 50/1.4 with a red index opposite the "4" is made in error. There is an entire subclass of legitimate 8-element production that has exactly that characteristic.


Steve

* As shown by the rear element per the comment.

[JollyGreen]

Does anyone know if my other old lenses are radioactive as well? I just picked up a Zeiss Biotar 58mm f2 (12 blade) and a Helios 44M-4 58mm f2.

[dbs]

Does anyone know if my other old lenses are radioactive as well? I just picked up a Zeiss Biotar 58mm f2 (12 blade) and a Helios 44M-4 58mm f2.

Hi Jolly

If you are so concerned why did you not check before purchase ?

[JollyGreen]

Hi Jolly

If you are so concerned why did you not check before purchase ?

I was never made aware that any lenses were radioactive until very recently. They don't advertise them as such.

[dbs]

Hi Jolly

Advertise now no but 50 yrs ago maybe.
The dangers as low as they are were not a known fact as today.

[PJ1]

Zeiss Biotar 58mm f2 (12 blade) and a Helios 44M-4 58mm f2.

They are not on my list of radioactive lenses but there are plenty of sites to check.

[UncleVanya]

Perspective:
Nick's Geiger Counter Page
1 micro sievert/Hour is roughly the same as the CPM * 0.0057

This video is of a seven element Takumar 50mm f1.4:

Youtu.be

Youtu.be

At 51 seconds in the count from the back of the lens is 22000 CPM (the scale indicator is on x1000 in the top of the display)
22000 CPM is roughly 125 micro sievert/hrs. EDIT, CPM can't be directly converted without more info on the equipment.

He later states no alphas, only beta and gamma. The second test tops at around 12000 CPM.

His background radiation measure is around 30CPM = 0.17 micro Sievert/hrs. EDIT CPM can't be directly converted without more details, but it does show a relative delta from background radiation.

The point of all this is to reinforce what Steve said, the measured radiation on the 8 element is inconsequential and does not point to the use of thoriated glass.

[PJ1]

Hello, Jolly Green. I had decided to stay out of this but your thread has taken a few unintended turns and I thought it might help if the external differences between the 7 and 8 element lenses were explained. @Wasp posted an image of two lenses – the 8 element on the right in his image and a supposed “hybrid” 8 element on the left. I have reproduced them below with the aperture ring/hyperfocal distance scale of the 8 element on the left and the supposed hybrid on the right. In the middle is the aperture ring and hyperfocal distance scale of the 7 element version (taken from the Pentax Forums site).

I am told there has been a lot written about “hybrids”. But there has also been a lot written to “prove” that the moon landings were a hoax.

Let’s just deal with what is on the hyperfocal distance scales of these lenses. You will note that the 4, 8 and 16 marks on the scale are the same to the right and left of the red diamond. They have to be symmetrical. Hyperfocal distance is exactly the same in front of and behind the focal plane. There is also a red IR mark.

On the 8 element version (left, below) the IR mark is just to the right of the 4.

On the 7 element version (centre, below) the IR mark is just to the left of the 4.

These differences are well known and they are a recognised way to tell the 8 element and 7 element versions apart.

On the supposed “hybrid” lens (right, below), the red IR mark is directly above the 4. In fact, it covers what would normally be the white 4 mark on a 7 element lens (compare it with the 7 element in the centre). Just to the left of this (where the red IR mark would normally be) is a white mark. What does it represent? Clearly it does not represent the 4 for the hyperfocal distance scale or there would be no symmetry in the distance between the 4 and 8 marks on either side of the red diamond. What has happened here with the supposed “hybrid” is that someone has taken a 7 element version, painted the white 4 mark red and overpainted the true IR mark white.



You can change aperture rings and switches and other stuff on a lens (if they fit) but that does not make it a “hybrid”. A true hybrid would have a different set of lens elements and groups. The 8 element has 8 elements in 6 groups (one group being the expensive “triplet”) and the 7 element has 7 elements in 6 groups (see below).



We can’t just swap elements in and out of a lens to create something new and expect it to perform to a certain spec. Optics is a science. But we also know that if the lens on the right above really is a hybrid, some of the lens elements or groups must be different to both the standard 8 element and the standard 7 element. Something must have been changed in the optics for the IR mark to have shifted.

Either that or it didn’t shift – a new IR mark was just painted on.

I know where the evidence points, but anyone is entitled to draw their own conclusions. I will also point out that the supposed “hybrid” has the same rear element presentation as the 7 element version. I believe the “hybrid” is just a doctored 7 element lens.

But I am willing to be proved wrong if someone can put up the “hybrid” elements/groups schema. The invitation is there for anyone to take up. It seems like a lot of trouble to go to for a lens that is not particularly rare (and I can't see how anyone could fiddle with the cemented triplet). But it would still need to go into the database.

I hope this helps in your search for an 8 element Takumar 50/1.4
Peter