[JollyGreen]

Hello all,

I'm new here, I am in the market to pick up one of these excellent old 50mm Super Takumars, but I have one question that I can't seem to find a definitive answer about online. Is the 8 element 50mm f1.4 Super Tak's made with thorium glass, or no? The radiation doesn't concern me, but I would like to know for certain, and I can't seem to find this information anywhere. I've seen photos where it seems like the original 8 element seems yellow, same as the 7 elements, and I'd just like to verify if they are also made with thorium glass.

Thanks!

[jbinpg]

My Super-Takumar 8-element has a yellow wash across the front element but it is not a thoriated lens, that was just the coating they used then. The lens only has one drawback: it flares and ghosts badly with a bright light source in the frame so the coating is not up to current standards. In all other aspects, it is stupendous. The focus to non-focus transitions are beautiful. Sample photo from today below.

.

[GQPhdFBI]

You can recognize the 8 and the 7 element taks by looking at the DoF scale.

The 7 element Takumars have the infrared focusing mark to the left of the numeral '4' on the DOF scale. The 8 element version has the mark to the right.

I believe both versions are radioactive.

[Paul the Sunman]

According to Stevebrot, no.

* The 8-element version was the very first version of the ST 50/1.4 and was made in fairly limited numbers before being replaced by 7-element variants for the rest of the product life. The 8-element lenses are never radioactive, are collectors items, and usually command a premium price. There are numerous ways to tell the two apart (rear element profile, weight, lens barrel markings, etc.). It is sort of a cult thing. The lens review on this site for the 8-element is helpful for sorting things out, it you are interested. Super-Takumar 50mm F1.4 (8-element variant) Reviews - M42 Screwmount Normal Primes - Pentax Lens Reviews & Lens Database

Read more at: Which lenses are radioactive and are they dangerous? - PentaxForums.com

[PJ1]

Paul the Sunman has it right. The 8 element version is not radioactive. And as GQPhdFBI said, the infrared focusing mark on the 8 element version is to the right of the f4 mark, while on the 7 element version it is to the left. Just be aware that there are some scammers out there who repaint marks to make a 7 element version look like an 8 element. But the attempts are fairly crude. If you have any doubts just post a link here and someone will be able to tell you if it is the real deal or not. I have the 8 element version and it is as good as they say.

[Wasp]

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



Re: Asahi Super Takumar 50mm 1.4 M42: Adapted Lens Talk Forum: Digital Photography Review

[JollyGreen]

Thanks all. I'm aware of how to tell the two lenses apart but here are my concerns:

-I've seen video online of a Geiger counter and an 8 element with it reacting to the lens. People seemingly have tested it.

-Thorium wasn't a coat on the lens, it was baked into the glass composition itself so if there is any yellow, it leads one to believe that it is thorium.

-it is concerning that I can't seem to find any definite data from the company itself regarding this fact.

My wife has thyroid problems and can't be anywhere near radiation. I wouldn't want to purchase (considering I already have a Nikon Z 50mm and other Zenit 85, 58, etc) without knowing without a shadow of a doubt there is zero thorium (which isn't just an alpha particle concern, but confirmed a beta and gamma particle concern also).

For mint condition I've found some for $375- $400 and I wouldn't want to waste that money without knowing for SURE. If it were true it weren't thorium, it would seem like the company would be proud to state that fact somewhere. But it sounds like they may have been cutting corners the whole time and are obscuring that data

[GUB]

Hello all,

I'm new here, I am in the market to pick up one of these excellent old 50mm Super Takumars, but I have one question that I can't seem to find a definitive answer about online. Is the 8 element 50mm f1.4 Super Tak's made with thorium glass, or no? The radiation doesn't concern me, but I would like to know for certain, and I can't seem to find this information anywhere. I've seen photos where it seems like the original 8 element seems yellow, same as the 7 elements, and I'd just like to verify if they are also made with thorium glass.

Thanks!

I now have 4 x 8 elements and they are all clear
Three of them are in the top row here -- So should I bleach my 50s - PentaxForums.com

[stevebrot]

-I've seen video online of a Geiger counter and an 8 element with it reacting to the lens. People seemingly have tested it.

Welcome to the Pentax Forums!

I would be interested in seeing that video if you still have the link.


Steve

[kypfer]

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

That alleged "hybrid" is clearly a fake. The figure 4 on the aperture scale should align with a white mark, not the red i/r index ... the marks have been repainted!

[stevebrot]

That alleged "hybrid" is clearly a fake. The figure 4 on the aperture scale should align with a white mark, not the red i/r index ... the marks have been repainted!

The photo does show the obvious rear element difference quite nicely. However, the existence of mixed-part-bin ST 50/1.4s is fairly well-established. I say fairly because accepting requires a certain amount of faith in @droo, the keeper of the Takumar Field Guide Web site and PF member. Below is a photo identified on that site as a late 8-element ST 50/1.4. Note the red IR index.



The image was lifted from 1 : 1.4 / 50 (358) 8 element - Takumar Field Guide and the descriptive text reads:

RHS ​(Above) Final large batch e.g. 1591XXX contains copies with available but irregular parts. The LHS of depth of field gauge shows the red IR marker placed correctly in relation to other markings to signify a 358 (this version), but, a 38700 DOF gauge plan (belonging to the next version) has been used to do it! The f=4 finds itself (misplaced) beneath the IR mark as a result. The font for numerals is oval and the 4 "open". This copy is an 8 element 358, one of possibly 3 - 4,000 final copies with this arrangement. The picture is SN 1591856 (without a product number and with a protruding rear lens). It is not a "hybrid" (because no true hybrid is possible); but a copy assembled from available parts that was not wasted, and it's special. A reminder of a time without wasteful attitudes?

Again, the lens in the photo from DPR is an obvious repaint of a 7-element lens, but confirming such requires a look at the rear element.
Addendum: IIRC, the thread discussion at DPR addressed and debunked the "hybrid" claim.

Steve

[7.62lew]

I did a quick search for geiger counters and some look fairly inexpensive. Or there may be someone local with one that could check the lens for you, like maybe the volunteer fire department or local hazmat team. Just make sure you can return the lens if it is radioactivve.

And please let us know if you do have one tested. I think one of my coworker is a volunteer fireman and I will make some inquires.

I have both a seven and eight element and my eight has no yellowing.

[Kozlok]

Hello all,
I've seen photos where it seems like the original 8 element seems yellow...

Thanks!

I have never seen an 8 element yellow like a thoriated lens would. All evidence I have seen suggests there is no thorium in this lens.

The coating on the front of the 8-element lens has a golden sheen to it, and in the right light, at just the right angle, it does look a bit like a yellowed lens. In your hand, you can clearly tell it's the coating, and it's not the same as the yellow seen in "yellowed" radioactive lenses. In a yellowed lens, moving the angle of the lens has very little effect on the color, whereas with the coating, it comes and goes depending on the angle; and has a sort of glowing look to it.

As a point of comparison, my early FA43 has a similar effect to the coatings, but they show a very clear aqua green color, instead of the golden color of the 8-element. Most of my DA lenses have a green tint that's greener than the FA43.

[JollyGreen]

Youtu.be

Youtu.be

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?

[PJ1]

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

The 8 element probably has lanthanum glass which is not very radioactive. The readings for the 8 element are only a little above background. Thorium glass gives the higher readings. The following is lifted from a file I have on radioactive lenses:

"Typical radiation levels can approach 10 mR/hr (100 μSv/h) as measured at the lens element's surface, decreasing substantially with distance; at a distance of 3 ft. (.9 m.) the radiation level is difficult to detect over typical background levels. For reference, a typical chest x-ray consists of about about 10 mR, a round-trip cross country airline flight exposes a passenger to 5 mR, and a full set of dental x-rays exposes the patient to 10 mR to 40mR.
Most smaller lenses with thorium elements are not very dangerous. However, thorium eyepieces are dangerous. They can give a very large alpha and beta particle dose to the cornea of the eye, causing cataracts and other problems. Normally these particles are stopped by skin, but the surface of the eye is quickly damaged by them, and at close range, the dose can be very high. "

I have a couple of radioactive lenses - the Takumar SMC 50/f4 and the Zeiss 80/f2.8 (P6 mount). There may be others. I doubt if the radiation is measurable outside the cupboard where my photographic gear is stored and doubt if it measures much more when I am using them. If there was a real issue I think there would have been a class action long ago. Bananas, brazil nuts, smoke detectors, granite bench tops and lots of other things around the home are also radioactive.