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10-12-2017, 08:47 AM   #16
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QuoteOriginally posted by dcshooter Quote
The upshot is that emission is not very high, and potential absorption is even lower (i.e. 0.2% of maximum annual exposure to the eye and 0.17% total body for an 8 hour a day user of the hottest lens they tested, a Zeiss Tessar).
Probably at least as important as these harm estimates is the fact that they were doing gamma spectroscopy. The common comment on radioactive lens threads is that the radiation is beta only, forgetting that decay products are always present and contribute significant gamma to the totals.


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10-12-2017, 10:12 AM   #17
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QuoteOriginally posted by dcshooter Quote
I'm suspecting one of two things happened here. The cement used on the element equivalent to the radioactve element in the Ks has a tendency to degrade and fog over time. The easiest solution is to grab the radioactive doublet form a Tak and drop it in. I've performed this repair multiple times for people, and as I mentioned above, they are 1:1 subs for each other. The other possibility is that leftover thorium elements from the Takumar series were recycled into K lenses until they were used up. I have a couple of smaples ofthe K myself which both test zero radiation.
I think it is just the takumar optics with bayonet, and not a repair job, because one of these lenses is more that 30 years in my possession, so probably less that 10 years old when I bought it, deteriorating cement takes usually more time,
10-12-2017, 10:13 AM   #18
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For anyone curious about alpha, beta, and gamma radiation, I had a Kodak Ektar and two 50mm Super Takumars that I tested with a geiger counter.

Kodak Instamatic Ektar lens: 50 mR/hr with no barrier.
Super Takumar lens: 500+ mR/hr with no barrier.
Super Takumar lens: 250 mR/hr with a plastic or aluminum rear cap barrier.
Super Takumar lens: 100 mR/hr with a lead barrier.

The ʻno barrierʻ readings are mostly alpha particles.
The ʻplastic or metal capʻ readings are mostly beta.
The ʻlead barrierʻ can only be gamma particles.

I donated two of the lesser lenses to our schoolʻs science department for chem and physics classes.
10-12-2017, 11:03 AM   #19
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What subtle engineering- madness in the magic quality of imaging with thorium-based lenses! They thowrium radiation in all directions, no one realizing how that radiation subtly alters the colors, exposure results, etc on the roll of film in the camera! Voile! Magic!

10-13-2017, 07:39 AM - 1 Like   #20
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QuoteOriginally posted by stevebrot Quote
Probably at least as important as these harm estimates is the fact that they were doing gamma spectroscopy. The common comment on radioactive lens threads is that the radiation is beta only, forgetting that decay products are always present and contribute significant gamma to the totals.


Steve
Exactly!

The daughter products of thorium decay accumulate in the lens and release other kinds of radiation.

Last night I had dinner with a friend who is an astronomer. I asked him if he'd seen any thoriated lenses. He'd only seen one once -- a Zeiss aerial photography lens -- but it caused quite a bit of trouble because the gamma rays from the lens created noise in the CCD sensor.
10-13-2017, 10:58 AM   #21
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Would this effect cause issues on a CCD Pentax camera? Has anyone ever observed it? Or maybe it's only relevant with astrophotography.
10-13-2017, 12:48 PM   #22
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QuoteOriginally posted by leekil Quote
Would this effect cause issues on a CCD Pentax camera? Has anyone ever observed it? Or maybe it's only relevant with astrophotography.
We did not discuss the particulars but the effect would be proportional to the total time between the reset of the sensor and the read-out of the sensor which would be the sum total of the exposure time and the time it typically takes to read out a frame (because even when the shutter is closed, the sensor is being pelted by gamma rays).

From what I've seen online, both CCD and CMOS sensors have some susceptibility to gamma rays but I don't know if anyone has tested an old thorium glass lens on a K10D, K1, or other camera to see if anything strange appears.
10-13-2017, 03:28 PM   #23
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Not quite so scientifically complicated is the manner of clearing the yellowing/ browning. Ultra violet from the sun will do it and leave your lens crystal clear again. Wrapping foil round it reduces the amount of radiant heat hitting the black surfaces but also reflects the light back out again, giving double the action! Here is my f1.4 Tak in the kitchen window.

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10-13-2017, 03:45 PM   #24
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QuoteOriginally posted by lensnut Quote
Not quite so scientifically complicated is the manner of clearing the yellowing/ browning. Ultra violet from the sun will do it and leave your lens crystal clear again. Wrapping foil round it reduces the amount of radiant heat hitting the black surfaces but also reflects the light back out again, giving double the action! Here is my f1.4 Tak in the kitchen window.
Yes, that will work, though many of us have had good results using the JANSJÖ LED desk lamp from IKEA. The JANSJÖ can clear a lens in less than two days rather than the week or more often required with direct sunlight.* In addition, the JANSJÖ does not subject the lens to the risk of excessive heat (causes oil/grease migration).
JANSJÖ LED work lamp - black - IKEA
I have cleared five badly yellowed thoriated lenses using the JANSJÖ and highly recommend it or something similar.

The method goes like this:
  1. Remove both front and rear lens caps
  2. Set aperture wide-open
  3. Unless sure that the yellowed elements are toward the front of the lens, cover the front element in aluminum foil, shiny side toward the glass
  4. Position the head of the JANSJÖ a few millimeters from the rear element (this is where the flexible "neck" comes in handy)
  5. Evaluate after 24 hours
Evaluate by looking through the lens at a sheet of white paper in good light. The paper should appear quite white when viewed through a new or properly cleared lens.


Steve

* UV light is often a part of the discussion, but make take from multiple sources related to radiation-induced "color centers" is that light energy is more important than wavelength per se and that visible spectrum white light works nicely. Heat may also be used if the glass is being treated by itself.

Last edited by stevebrot; 10-13-2017 at 03:51 PM.
10-14-2017, 01:57 AM   #25
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Misinformed

There is a boatload of misinformation about this. Using a radioactive lens for 8 hours has been estimated to be about as harmful as two x-rays. Doing this everyday might not be so good. Most sources on the internet claim radioactive lenses are only emitting Alpha rays, which is absolutely false. Beta and Gamma rays are being emitted at high levels (see:
). The lenses are HOT. Don't delude yourself, because the qualities of the glass are divine for sure, that you can get away with using radioactive lenses forever without a risk. Nobody's ever reported ill effects from radioactive lenses... because nobody ever knows what caused their cancer. Nobody's ever sought out the answer because there is great financial reason not to, and in fact there is great financial reason to hide the truth. In fact, until the 1960's, radioactivity was pretty much not known to be harmful or even suspected to be harmful.Think about it.
10-14-2017, 03:12 PM   #26
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QuoteOriginally posted by dcshooter Quote
The only one spouting misinformation is you.

I've referenced an article based on actual research published by a reputable lab in the department of physics in a world-class university that fully takes into account Beta and Gamma emissions from Thorium and its daughter products in determining actual exposure rates from lenses. You, on the other hand, have a guy who is best known for swearing on Youtube being freaked out because he doesn't know how to interpret the readings on a Geiger counter.

The dose from a regular chest X-ray is .1mSv. A chest CT scan is approximately 7mSv.

The study referenced above estimates full body exposure for a photographer using the lens 8 hours a day every day to be .17mSv per year. Considering average background exposure is .01ms/v per day, this works out to being equivalent to an extra 2.5 weeks of background radiation per year, and only .17% of the extremely conservative Swedish guideline for maximum radiation exposure per year.

In short, the figures you "quote" are utter horse manure and are off by roughly a factor of 500.

Take your hysteric fearmongering elsewhere.

Also, if you use the UNCEAR estimate of a 5.5% increase in risk of cancer per Sv, even an 8 hour a day user would be looking at less than .1% increased risk, i.e. so low as to be indistinguishable from statistical noise.
Actually you've made the incorrect assumption that my only source is the YouTuber. You've also made the assumption that anyone actually knows what a safe level for exposure is when in fact, the data is very incomplete with multiple factors making it difficult to distinguish causation.

The jury's still out I suppose, but I for one will avoid the beta and Gamma rays the best I can.. which is why I posted that video - because many have posted all over the internet that only alpha rays are emitted. You completely missed my point.
10-14-2017, 08:46 PM   #27
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QuoteOriginally posted by vyoufinder Quote
Actually you've made the incorrect assumption that my only source is the YouTuber.
That is good to know, because he is quite misinformed.

As for the jury being out, that is a strange statement to make, but whatever suits your comfort level. Being you are in Moab, I can understand your concern about total exposure given the risk from soil radon and uranium ore dust in your region.


Steve

(...lots of radon potential in my crawlspace...I don't go down there...)
10-15-2017, 07:27 AM - 1 Like   #28
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QuoteOriginally posted by vyoufinder Quote
Actually you've made the incorrect assumption that my only source is the YouTuber. You've also made the assumption that anyone actually knows what a safe level for exposure is when in fact, the data is very incomplete with multiple factors making it difficult to distinguish causation.

The jury's still out I suppose, but I for one will avoid the beta and Gamma rays the best I can.. which is why I posted that video - because many have posted all over the internet that only alpha rays are emitted. You completely missed my point.
There probably is no "safe" level of radiation but that does not imply that every incremental exposure to thoriated Takumars (or air travel or bananas) is "dangerous". Unless you believe that getting less radiation exposure is more dangerous (don't laugh because some people do believe that), the worst case scenario is a linear dose effect in which each added unit of exposure brings an added chance of cancer. It's then a matter of using the copious data on the likely coefficient of that linear effect and the likely dose from the proposed activity (i.e., using a hot lens some hours per year). As the data from the article cited by dcshooter shows, the dose from these lenses is quite modest even compared to background radiation.

BTW, if you actually intend to "avoid the beta and gamma rays the best you can", then leave Moab Utah because the geology of the area makes it susceptible to high radon-levels (which do have documented dangers from exposure) and Moab's higher altitude (and latitude) increases resident's exposure to cosmic rays.

I think we all agree about the importance of managing risk but society's current fixation on safety seems to be creating it's own category of danger.

Last edited by photoptimist; 10-15-2017 at 08:21 AM. Reason: typo
10-15-2017, 07:35 AM   #29
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QuoteOriginally posted by photoptimist Quote
There probably is no "safe" level of radiation but that does not imply that every incremental exposure to thoriated Takumars (or air travel or bananas) is "dangerous". Unless you believe that getting less radiation exposure is more dangerous (don't laugh because some people do believe that), the worst case scenario is a linear dose effect in which each added unit of exposure brings an added chance of cancer. It's then a matter of using the copious data on the likely coefficient of that linear effect and the likely dose from the proposed activity (i.e., using a hot lens some hours per year). As the data from the article cited by dcshooter shows, the does from theses lenses is quite modest even compared to background radiation.

BTW, if you actually intend to "avoid the beta and gamma rays the best you can", then leave Moab Utah because the geology of the area makes it susceptible to high radon-levels (which do have documented dangers from exposure) and Moab's higher altitude (and latitude) increases resident's exposure to cosmic rays.

I think we all agree about the importance of managing risk but society's current fixation on safety seems to be creating it's own category of danger.
Actually, I've left this place many times for that very reason. I've also tested for radon all the places I frequent, and luckily I am ok there. The biggest danger I see with living in this area is when the wind blows, it blows tailings. I leave town for the wind or hide from it since inhaling the particulates probably poses the most danger. The tragedy of the mining industry is that the entirety of the profits made mining are chump change compared to the taxpayer cost of cleaning it up and covering the medical bills, lawsuits,etc. from their mining. It would make more sense financially if the taxpayers just paid the miners double what they would make mining to stay away. This was not a concern during the uranium boom. The effects of radiation were unknown at the time. However, now that we know, and we know the pattern of the mining companies declaring bankruptcy as soon as it's time to clean up, it's kind of ridiculous to see the problem being repeated.


Last edited by vyoufinder; 10-15-2017 at 07:45 AM. Reason: added video of interest
10-15-2017, 07:28 PM   #30
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QuoteOriginally posted by vyoufinder Quote
This was not a concern during the uranium boom.
Your statement reads as if the "boom" is over. Utah is gearing up for another uranium boom, from what I understand.


Steve
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