You all realize that bananas, potatoes, and even beer is radioactive due to the presence of the naturally occurring K-40 (potassium 40) isotope, right?
Yeah, but that's one of those semi-stable isotopes with exceptionally long half-lives. K-40 has a half life of 1.25 billion years! The dose in a banana is about 0.1µSv, or 0.0000001Sv. For the average human, radiation doses under 100mSv (0.1Sv) per year have no measurable health effects. You would need to eat one million and one bananas in a year to experience the most minimally measurable health effect due to potassium-40 radiation exposure. (I actually don't think that is humanly possible, to eat that many bananas.)
All true, Jon, although another way of putting it is that the Nuclear Regulatory Commission limit on dose to the public (above background) is 1 mSV, which, I agree, is still a lot of bananas :-).
My point was that we are exposed to many sources of radiation, natural and man-made, every day. The implication (in some posts) that Fukushima caused some measurable increase in the dose from lenses manufactured in Japan is bogus. Discussion of radioactive lenses isn't really meaningful unless you consider the associated dose, which is likely to be very small, if measurable at all.