Regarding the Asahi Super-Takumar 50 / 1.4:
I don't know what you're detecting, but if you truly have 8-element Super-Takumar 50 / 1.4 lenses then I highly doubt that it's Alpha radiation from Thorium. What is your method of testing? Is the detector shielded from other sources of radiation during the test? Be aware that most inexpensive detectors commonly available do _not_ detect Alpha radiation at all and you should check the specifications. Furthermore, I would more likely suspect that your lenses are 7-element and not 8-element to begin with. What evidence do you have that these lenses are 8-element? Be aware that even the pages on Pentax Forums contain inaccuracies in their descriptions of the visual differences. In particular, the statement "This 8 element version can also be identified on the slightly protruding rear lens element and on the stop down switch, which is marked A M (rather than Auto Man as on the later versions)." is inaccurate -- the rear element of the 7-element also protrudes, though not as much as the 8-element, and the early 7-element variant is also marked A M. The early 7-element (37800) is much more visually similar to the 8-element than the later 7-element (37801) is -- there is even overlap in serial numbers, so you can't judge based only on that -- my 8-element has a higher serial number than my earliest 7-element has. Have you at least weighed the lenses (without caps) and compared between 7- and 8-element examples? The 7-element weighs less than the 8-element -- based on my few examples, the 8-element weighs more than 240g, while the 7-element weighs less than 240g, even as little as 230g. I haven't yet bought a detector so I can't test mine at this time.
Even if your three 8-element examples are somehow radioactive by some other source (other than Thorium in the glass), that doesn't mean that _all_ 8-element examples are. Post the serial numbers, post the weights, post the readings. This page loses credibility when one person tests a few lenses and then makes a broad statement about all of them.
22.214.171.124 19:02, June 22, 2020 (UTC) A Super-Takumar collector and user
You may note that Marco is the _only_ person claiming that any 8-element lenses are "radioactive". I have seen no one else do so, and there are others who are much more authoritative who have tested their lenses for all four common types of radiation and have detected none, not even with much better detectors than Marco shows. The 8-element Super-Takumar 50 / 1.4 does not contain any radioactive elements and did not leave the factory emitting radiation. Any radiation Marco might be detecting is either not being emitted by the lens, or something happened after these lenses left the factory. One thing we know for certain that all three lenses he mentions have in common is that he has them and he serviced them. It is far more likely that if his lenses are emitting radiation, that he caused them to himself. I am further wondering why the lens he shows in the video appears to be on a rug. I intend to get a detector and test my 7-element (I have three) and 8-element (I have one) examples as well as all my other Super-Takumar lenses, but it's not a high priority. I recommend you test yours as well if you are concerned (even though there is nothing to be concerned about). Marco should also get his lenses tested by someone else. As far as anyone knows Marco's are the _only_ "radioactive" 8-element Super-Takumar 50 / 1.4 lenses in existence.
126.96.36.199 20:59, June 24, 2020 (UTC)
Buddy, stop your nonsense and get yourself a Geiger counter. Seriously, stop smearing mud on your face, it's not doing you any good.
Marco 188.8.131.52 10:13, June 28, 2020 (UTC)
A few more 8-element Asahi Super-Takumar 1:1.4 / 50mm results[edit source]
I have five examples and I have tested them for "radioactivity". I conclude that while some do test "positive", they have much lower readings than the 7-element examples and 1:1.8 / 55mm examples I have. 1062277 No 1179683 Yes 1385317 Yes 1482558 Yes 1582176 No The first of these appears to be what the Takumarology page refers as "variant C", while the others are "variant D" -- the visible differences being the typeface used for the various markings and the DOF scale.
Regarding SMC Takumar 85/1.8[edit source]
Are we sure? I have tested mine, serial n. 5228527, and I cannot detect any radiation. Note however my Geiger counter only detects Beta and Gamma particles, not Alpha.
- Hello, the 85/1.8's dose should be really small compared to, for instance, Takumar 50/1.4. However, it's still measureable - see the added link.
SMC Takumar 85/1.9[edit source]
I just tested my SMC 85mm f1.9 and did not detect any beta or Gama rays.
- The SMC 85/1.9 is an older Sonnar(ish) design which is not radioactive - I've tested one.
Topcor RE GN 50/1.4[edit source]
The article states "Lanthanum glass" which doesn't match with the actual measurement. The measured values point to Thorium glass. Any sources for the Lanthanum glass statement?
Zenitar-M 50mm f1.7[edit source]
The article stated "Lanthanum glass", although I couldn't measure any increase compared to natural background. Should it really be present on the list?
Mitakon (Zhongyi) 50mm f0.95 Ver II Dark Knight[edit source]
This lens has actually been tested by myself for beta & gamma radiation but has not been found to emit any detectable quantity. Please provide evidence of the contrary or remove this lens from list of radioactive ones. Reading somewhere that a lens may contain elements that could be radioactive is not enough to include it in the list.
Industar 61 L/Z MC[edit source]
The lens is NOT radioactive, as the myth says (L is for Lanthanum. Only 0,089 % of total naturally found Lanthanum (La-138) isotope is radioactive, and even it has half-life of 105 billion years.