Pentax Takumar Lens Radiation for Pentax 6x7 Lenses

baronkatz · Sep 22, 2015

Hello All!

I've been doing photography for 15+ years now. I shoot 35mm, Medium Format and Large Format. For most of my fashion and portrait work I use a Hasselblad 501C currently but am looking to get a Pentax 6x7, 67 or 67II with a 105mm F2.5 but I read on this site http://camerapedia.wikia.com/wiki/Radioactive_lenses that the Takumer 105mm f2.5 is made with radioactive Thorium glass.

My question is whether this is for ALL the 105mm f2.5 lenses or only the older Takumar branded ones (the newer ones that just say Pentax are not radioactive)? When did Pentax switch over to non-thorium lens elements? How can I know which ones don't have it? Were there any other lenses that were radioactive?

Also I am debating between buying the three different Pentax camera's. The II is obviously more expensive but I want a really bright WHITE viewfinder. I can't stand it when they have the split finder and the yellowing. Do all of them have that? Thank you!

The reason for switching is that I really love the Bokeh, Contrast and look you get with the 105mm F2.5 Takumar and many other Pentax lenses, it's very similar to the 110MM/F2 Hasselblad Zeiss lens but for a lot less money. I can't afford the Hasselblad Zeiss lenses that I really want so this is a much cheaper option + it seems more ergonomic and compact to travel with.

mweintraub · Sep 22, 2015

This: http://nortega.com/fastest-tool-to-clear-yellowed-thorium-lenses/

I bought this lamp, but haven't de-yellowed my 105mm yet.

Alan9940 · Sep 22, 2015

If you want the brightest viewfinder available on the Pentax 67, then you'll need the II. I have both an older MLU Pentax 67 and the newer II and the latter is significantly brighter and easier to focus; for me, anyway.

Good luck!

baronkatz · Sep 22, 2015

mweintraub said:
This: http://nortega.com/fastest-tool-to-clear-yellowed-thorium-lenses/

I bought this lamp, but haven't de-yellowed my 105mm yet.

I'm not worried about the yellowing as I am the radiation from the lens.

Alan9940 said:
If you want the brightest viewfinder available on the Pentax 67, then you'll need the II. I have both an older MLU Pentax 67 and the newer II and the latter is significantly brighter and easier to focus; for me, anyway.

Good luck!

I guess I'm just wondering whether it's worth paying 2-3 times more. The 67 II does have the cleanest and newest look, but it is a lot more money... Are the other viewfinders fairly yellow compared to it? I know this isn't just age - my Leica M3 has the brightest viewfinder I've seen from almost any rangefinder and has practically no flair and it's a 50s-60s camera. For SLR's for some reason it was trendy until the 1990's to have a Yellow viewfinder like on my 110B Polaroid, sooo difficult to focus...

StephenT · Sep 22, 2015

"I know this isn't just age " One less reason to worry about the radiation!! Just like me!

I really wouldn't worry about the thorium; somewhere I had the stats on it but they have wandered off in the filing system somewhere, but I recall that it was relatively insignificant.

I have several of the 67 and 6x7 bodies and the screens can be a little dark, along with some of my other older beauties, but I haven't yet seen a 67II for a giveaway price. When I do, it'll have a new owner. Don't forget you've got that depth of field info on the lens - I have used it in really dim light and it works fine. Mirror lock up and heavy tripod come in handy as well!

Chrismat · Sep 22, 2015

I just looked at the Camerapedia site, and I've had my 105 2.4 lens since I bought my Pentax 6X7 in 1983, and it is still is as clear as the first day I used it. I don't know if others have had yellowing in their 105s, but mine has been fine. I do own a Takumar 55 1.4 M42 lens that did have the yellowing, but I cleared that out.

BAC1967 · Sep 22, 2015

Do you worry about eating bananas or flying on airplanes, if not then don't worry about thorium glass. You will get less exposure from the lens than bananas and airplanes. If you crushed the lens into a fine powder and ate it you may have a problem. Considering how often you would likely have the lens close to your body, the harm from the radiation you would receive is far less than many other things you encounter on a daily basis.

cuthbert · Sep 22, 2015

Radioactive glass is good, it gives your superphotographer's powers...Peter Parker docet!

Alan9940 · Sep 23, 2015

baronkatz said:
I guess I'm just wondering whether it's worth paying 2-3 times more. The 67 II does have the cleanest and newest look, but it is a lot more money... Are the other viewfinders fairly yellow compared to it? I know this isn't just age - my Leica M3 has the brightest viewfinder I've seen from almost any rangefinder and has practically no flair and it's a 50s-60s camera. For SLR's for some reason it was trendy until the 1990's to have a Yellow viewfinder like on my 110B Polaroid, sooo difficult to focus...

Wow...I just looked and the prices for the 67 II certainly have gone up quite a bit from when I bought mine just a few years ago! Yellow viewfinder? I've had my prior 67 since the 1980's and the viewfinder is crystal clear; albeit dim when compared to the II. If you have young eyes, then I wouldn't worry too much about the lack of brightness with the older 67's; 30 years ago I never had a problem focusing the 67. If you do decide to go with a model prior to the II, then I'd highly recommend staying away from the non-MLU bodies. These cameras have HUGE mirrors and shutters and for absolute sharpness at any shutter speed and certainly in the critical range, locking the mirror up should be sop.

Best regards,
AlanH

Theo Sulphate · Sep 23, 2015

baronkatz said:
I'm not worried about the yellowing as I am the radiation from the lens.

There is nothing to worry about; the amount of radiation is insignificant.

If you look at several of the radiation charts available online, you'll see that just your daily exposure to radiation (just by being on the planet) is comparable to the radiation of this lens. As a previous poster wrote, eating bananas or flying on a plane will expose you to more radiation.

So remember this: a little radiation never hurt anyone.

baronkatz · Sep 23, 2015

Theo Sulphate said:
There is nothing to worry about; the amount of radiation is insignificant.

If you look at several of the radiation charts available online, you'll see that just your daily exposure to radiation (just by being on the planet) is comparable to the radiation of this lens. As a previous poster wrote, eating bananas or flying on a plane will expose you to more radiation.

So remember this: a little radiation never hurt anyone.

Even if this is true, it's all accumulative, a little bit from this, a little from that, it all adds up. I read somewhere that holding the lens in your hand for an hour is equivalent to getting a chest x-ray. If so getting a chest x-ray everyday (if I held it for an hour a day hypothetically speaking) is not that great for you. There are other problems - If I dropped the lens and it shattered, the dust from it would not be good at all...

Someone from another forum post wrote "Thorium - an Alpha emitter - decays over time into daughter products that are Gamma emitters (not Beta). It's when this happens (over decades) that the lens becomes hazardous. Alpha particles can be blocked by a thin metal lens cap. Gamma particles go on and on like the proverbial battery bunny, and will even pass through a Lead brick. Those radioactive particle emissions also change the structure of the glass and it darkens to a light amber colour over time.Alpha particles can cause more tissue damage than Gamma particles, but only when in close proximity. It's the penetrating ability of Gamma radiation that poses a greater hazard.
In short; if there's no browning of the glass then no worries! Although it's reported that the discolouration can be reversed by exposure to strong UV. I'm doubtful of that myself, but it may be so."

Either way - even if it didn't do me harm. For peace of mind - I want to know WHEN Pentax had turned to using non-thorium glass for their 105 f2.5. If this was with the later lenses (IE 1980s ones that said just Pentax without the Takumar name) then I want to know which ones. There must be someone who knows this...

pdeeh · Sep 23, 2015

we're all doomed

cuthbert · Sep 23, 2015

pdeeh said:
we're all doomed

Seriously, a lot of people are even scared to touch a 7 elements Takumar because of the radiations, another "scary" lens is the Canon FD 35mm f2 with concave nose (even more radioactive than the Taks) but all these lenses were used for many decades by thousand of professional photographers, if they were dangerous we would have known the problem as the "photographer's syndrome" (like the Gulf syndrome)...ironically no Leicaman is scared by using the Summicron I and II that are as radioactive as the lenses I talked about.

baronkatz said:
Either way - even if it didn't do me harm. For peace of mind - I want to know WHEN Pentax had turned to using non-thorium glass for their 105 f2.5. If this was with the later lenses (IE 1980s ones that said just Pentax without the Takumar name) then I want to know which ones. There must be someone who knows this...

I have no clue about medium format Taks but I know that for the 50mm f1.4 used on Spotmatics they introduced the thorium element when they discontinued the original 8 elements design (too expensive) , supposedly the lens has become less radioactive and the 8 blades is the less radioactive of the range, SUPPOSEDLY when they introduced the K mount they changed the material (but not the formula, even if I have problems believing that), although I can't say the K mounted lenses aren't radioactive a lot of people think this way.

Also, on another board an old member said that for recognising if a lens has a thorium element you have to put it diagonally on a piece of paper, if this looks brown through the lens it's thorium.

baronkatz · Sep 23, 2015

cuthbert said:
Seriously, a lot of people are even scared to touch a 7 elements Takumar because of the radiations, another "scary" lens is the Canon FD 35mm f2 with concave nose (even more radioactive than the Taks) but all these lenses were used for many decades by thousand of professional photographers, if they were dangerous we would have known the problem as the "photographer's syndrome" (like the Gulf syndrome)...ironically no Leicaman is scared by using the Summicron I and II that are as radioactive as the lenses I talked about.

Summicrons with SN after 105xxxx do not use radioactive glass. IE any lenses made before 1953 do but not after. Thorium glass was really used to make faster lenses cheaper to manufacture. Leica stopped its use in the early-mid 50's, as did Zeiss (except for Jena, DDR, where they were cheap as well), Schneider, and others. Japanese manufacturers kept using it until the 1970s or 1980s even... That's the biggest difference. It's much easier to track this stuff with Leica as well... and yes I use an M3 and think it's the greatest camera ever made.

I'm sure it's not THAT dangerous but why have an extra piece of radiation in the house? What if you drop it and the glass shatters? There is no way to "prove" that the lens contributed in any way to anything like cancer, but it could be one small thing in a 100 others that might. The more you eliminate the better. Even IF it's 99% safe, it's about piece of mind if that makes sense to anyone...

DannL. · Sep 23, 2015

I used the Takumar 1.4 for quite a while. And now, years later . . . I'm completely deaf in my right eye.

baronkatz · Sep 23, 2015

Anyway thank you for all your answers - you've been a huge help! If anyone has a Pentax 6x7, 67, or 67II with a SMC Pentax 105 2.4 - please PM me as I'm looking for one and would be open to trading for my drum scanning services.

cuthbert · Sep 23, 2015

baronkatz said:
Summicrons with SN after 105xxxx do not use radioactive glass. IE any lenses made before 1953 do but not after. Thorium glass was really used to make faster lenses cheaper to manufacture. Leica stopped its use in the early-mid 50's, as did Zeiss (except for Jena, DDR, where they were cheap as well), Schneider, and others. Japanese manufacturers kept using it until the 1970s or 1980s even... That's the biggest difference. It's much easier to track this stuff with Leica as well... and yes I use an M3 and think it's the greatest camera ever made.

I'm sure it's not THAT dangerous but why have an extra piece of radiation in the house? What if you drop it and the glass shatters? There is no way to "prove" that the lens contributed in any way to anything like cancer, but it could be one small thing in a 100 others that might. The more you eliminate the better. Even IF it's 99% safe, it's about piece of mind if that makes sense to anyone...

Actually the Summicron II has Lanthanium that like Thorium is mildly radioactive (it was also used by the Soviet in the Industar 61, that is casually the sharpest RF lens they made).

Having said that I have more than a CZJ glass and it outperforms anything made by Nikon and Canon, some people consider the 50mm f1.4 as good as the Summilux R, and the use of Thorium doesn't mean a glass is cheap, on the contrary for it's a warranty of sharpness.

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Also, I have many vintage watched with the dial painted with RADIUM, these are really dangerous if you inhale the vapour of these radioactive varnish, until 2003 it was common practice in that industry to use tritium for dials, according to you we should stop using any watches with luminous dial built more than 13 years ago.

baronkatz · Sep 23, 2015

cuthbert said:
Actually the Summicron II has Lanthanium that like Thorium is mildly radioactive (it was also used by the Soviet in the Industar 61, that is casually the sharpest RF lens they made).

"Contrary to often seen statements to the otherwise, lenses containing lanthanum are not appreciably radioactive - lanthanum is only 1/10,000th as radioactive as thorium. Radioactivity in lanthanum containing lenses is due to the intentional inclusion of thorium in the optical glass mix." IE Lathanium is not really that radioactive at all... Almost undetectable even...

cuthbert · Sep 23, 2015

baronkatz said:
"Contrary to often seen statements to the otherwise, lenses containing lanthanum are not appreciably radioactive - lanthanum is only 1/10,000th as radioactive as thorium. Radioactivity in lanthanum containing lenses is due to the intentional inclusion of thorium in the optical glass mix." IE Lathanium is not really that radioactive at all... Almost undetectable even...

Despite of what camerapedia writes Lanthanium IS radioactive, like all the heavy metals of their group in the table of elements:

http://www.tandfonline.com/doi/abs/10.1080/14786435708231721

Poisson Du Jour · Sep 23, 2015

If you are (irrationally) concerned with the perils of radiation, seek out the newer generation SMC Pentax 67 lenses that do not have thorium elements, and which have better optical performance to boot. Takumars are very ordinary, unremarkable. The subject of "radioactive lenses" has been flogged to death for decades. Thorium was used in many early Asahi Pentax lenses and miscellaneous items, like the 6x7 right angle finder (but not the later Pentax 67 right angle finder). Early Asahi Pentax microscopes also used thorium lenses.

Sent from my LG-D855 using Tapatalk

baronkatz · Sep 24, 2015

Poisson Du Jour said:
If you are (irrationally) concerned with the perils of radiation, seek out the newer generation SMC Pentax 67 lenses that do not have thorium elements, and which have better optical performance to boot. Takumars are very ordinary, unremarkable. The subject of "radioactive lenses" has been flogged to death for decades. Thorium was used in many early Asahi Pentax lenses and miscellaneous items, like the 6x7 right angle finder (but not the later Pentax 67 right angle finder). Early Asahi Pentax microscopes also used thorium lenses.

Sent from my LG-D855 using Tapatalk

Thank you - this is very helpful!

Vitoret · Sep 24, 2015

I had a Takumar 50mm f1.4 with thorium lens and i really love it.. after reading about low radioactivity risks on the web i was not that worried.
After one year or so shooting with it, i had the chance to let my lens be tested by a specialyzed technician i met (he checks radioactivity for hospitals and public structures).
He told me that my lens emitted really high alpha radiations form the back element but i had not to worry since alpha are easily blocked by the camera body. Looking directly into the rear of the lens for some time could cause eye damages (but this is not a problem).
The real problem was that he detected beta and gamma rays too. Thorium perils emitting beta and gamma too.
Gamma rays were not that high but they are ionizing rays that can (eventually!) split cell connections (i'm italian sorry for my bad english here) and cause problems.
Gamma rays go through the body of the camera and through your body very easily. I asked him if it was safe to take it with me on my 7 days trip, he said i had to avoid prolonged usage and to store it at home in some thick metal container to isolate the gamma.

This is my experience and i really don't want to scary anyone.. anyway i suggest to let your thorium lenses to be checked by an expert.

After the test i've sold my lens and bought the first version of Super-Takumar 50 f1.4 (8 element) thorium free..

cuthbert · Sep 24, 2015

The gamma rays from the thorium lenses aren't strong enough to impress your film (the ones from a X ray scan are) so there is no harm.

Vitoret · Sep 24, 2015

cuthbert said:
The gamma rays from the thorium lenses aren't strong enough to impress your film (the ones from a X ray scan are) so there is no harm.

I guess x-rays are strong radiation in "little" time.

With a camera the only problem could be the accumulation of low insensity radiation over a LONG time since our body accumulates radiation over time. It all depends on intensity,time and how the body reacts to it.
My lens had a gamma range of 1,5 meters so even if not much intense i would not let the camera sit next to me all day..

Anyway it would be interesting to see if a film roll in a camera with thorium lens starts fogging with time..

DannL. · Sep 24, 2015

http://petapixel.com/2012/10/11/a-look-at-the-radioactivity-of-old-manual-lenses/

https://www.youtube.com/watch?v=3ozOMssiP2E

An interesting video. Makes my eye hurt.

Pentax Takumar Lens Radiation for Pentax 6x7 Lenses

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