Somebody settle this factually

<p>I've seen postings here and there claiming that the Mamiya Sekor 55mm/1.4 lenses (pre-SX) made for the TL and DTL series cameras contain some glass with radioactive thorium and are therefore subject to yellowing.<br /><br />Has this radioactivity and yellowing been substantiated by anyone who has credibility in these matters? (As opposed to the kind of people who broadcast their own and each other's guesses and errors) This is about the glass itself; yellowish lens coatings are another matter.<br /><br />What about the situation with 55mm/1.8 and 50mm/2 Mamiya Sekor lenses of that era?</p>

I don't know if this is authoritative enough! I accept this (that thorium was used in lens design) as fact.. what was used on a particular Mamiya lens, I must plead ignorance!

 

http://camerapedia.wikia.com/wiki/Radioactive_lenses

<p>I know of other lenses (e.g., certain M42 Takumars) that were measured to be radioactive by people competent to do it. Thorium oxide can enhance some properties of optical glass. Sorry if I was unclear about that.</p>

<p>In 1970 at college I bought a Mamiya Sekor 1000DTL with a 55mm 1.4 Mamiya lens. I was a geology/engineering student then and we used x-ray diffraction gear and worked with various radioactive ores a lot. I never noticed any readings coming from my lens, not that I particularly looked nor took the opportunity to measure my stuff. I know the camera was always lying about as were the counters, so I would suspect I might have noted something by mere serendipity had there been thorium in the lens.</p>

<p>It is altogether possible I just never noted nor had the happenstance. So, for what it's worth I say I don't have any hard evidence but suspect 'not' in my case.</p>

<p>Jim M</p>

<p>I have a 55/1.4 pre-SX Mamiya lens. I will have to look for it. Some lenses even older than the Mamiya have yellowing of the cement used to attach elements and are not radioactive. The worst lens I have for yellowing must be the 28/2.5 Minolta MC Rokkor. My favorite radioactove lens is a black front 35/2 Canon FD SSC with the concave front element. I gave it the light treatment with a CFL bulb and irt is very close to clear. I have four of the later 35/2 New FD lenses and they are very good too but the FD SSC is one of a kind. </p>

<p>Anyone who has this lens in the metro Boston area, feel free to contact me, and I'll point my Geiger counter at it.<br>

(It certainly confirms that my Leica Summicron 50/2.0 is radioactive, along with my RE GN Topcor 50/1.4.)</p>

<p>I have the Mamiya/Sekor 1:1.8 mounted on the 1000 DTL, I dont see any yellowing on this model, not unless ever so slight that I dont? I just used the lens the other day mounted on my Pentax K110D, I didnt notice any issue on the pictures...I'll have to see if the lens glows at night! :)</p>

<p>~Jack</p>

 

<p>I think that little physical harm to you from any of these lenses is likely to result so long as you don't carry it around in your underwear.</p><div></div>

<p>I don't see any sign that my own Mamiya Sekor 55mm/1.4 lens (Serial Number 12x,xxx, black, bought used with 1000DTL camera) has yellowed.</p>

<p>Bananas are radioactive, in fact the exposure of workers in nuclear facility s are rated in bananas read this http://en.wikipedia.org/wiki/Banana_equivalent_dose, I have the Canon FD 35mm f2 Thorium lens and my eldest son who is a Physicist tells me as long as I don't sleep with it under my pillow it's OK, anyway if it was so radioactive it would fog film.</p>

<p>I have the lens in Cosinon and Rikenon brands (the 1.4), and the Mamiya-branded 1.8. No yellowing on any of them. I also have yellow Takumars, I would have noticed if those lenses were yellow. They seem similar in make-up to the Rokkor 58mm 1.4 lenses, which do all seem to have a very faint amber tint, but I assumed that had to do with coatings and not an age-related yellowing of the elements themselves.</p>

 

<p>I suggest you look at this http://www.orau.org/ptp/collection/consumer%20products/cameralens.htm, and to my knowledge also the Canon FD 35mm f2 with the concave front element there were also several others until the Japanese government health and safety agency banned their manufacture due to health and safety issues with the workers grinding the glass.</p>

<p>Radioactivity from glass in camera lenses is as likely to harm you as the radioactivity from the damaged power plant in Japan if you live in Omaha (or even L.A.) Granite countertops usually are more radioactive.</p>

<p>That's correct Wayne, also Brazil Nuts are more radioactive</p>

<p>I would still appreciate a factual answer to my original question.</p>

<p>Bob- my eldest son is a nuclear physicist who has BSc and MSc degrees from the University of Manchester here in England he has looked into this matter for me and he tells me the risks are so small as to be inconsequential,which is good enough for me, if you require incontrovertible scientific proof I suggest you pay to have a qualified organization or person to research the matter for you and produce a report on their findings and not ask the question on internet forums where you are going to get plenty of opinions from unqualified people, but they are just opinions, not facts</p>

<blockquote>

<p>also Brazil Nuts are more radioactive</p>

</blockquote>

<p>And bananas.</p>

<p>Hello,<br>

New to this forum and noticed the question on the Mamiya 55mm f/1.4 lens regarding Thorium and radioactivity. It just so happens that I was preparing one of these lenses (pre-SX, f/1.4 auto Mamiya Sekor M42 serial number 86795) for sale a couple of days ago and noticed the yellowish cast to the lens elements, similar to the color I have seen on Takumar lenses. Sure enough, when the lens was exposed to my rate counter, I found it happily throwing off Beta particles and Gamma rays. Here is a link to a photo of my test setup: <a href="http://billrogers.com/mamiyaf14.jpg">Mamiya f/1.4 lens</a> Hope this settles the issue, although maybe not all samples of this lens will respond the same?<br>

Bill</p>

 

The thing though is not whether or not other things are more radioactive, but that all these things add up. Take pictures with that lens of someone you're eating Brazil nuts and bananas off a granite countertop with, and you top up your 'still safe - but don't kid yourself thinking we actually know what's safe - exposure dose' more quickly.<br>;-)