Originally Posted by YJD
What??? Serious?
Yes, from the Thorium. Thorium was added to the glass of many high quality lenses. The upside to a radioactive lens is that it has a good chance of being very good.

I would be concerned it if were the viewfinder.
Edit:
SMC Takumar 50mm f1.4 (Asahi Optical Co.)
Super Takumar 35mm f2.0, 50mm f1.5, 55mm f2 (Asahi Optical Co.)
Super Takumar 6x7 105mm f2.4 (Asahi Optical Co.)
Super-multi-coated Macro-Takumar (Asahi Optical Co.)
These are from the ORAU site. Here is a link at the Oak Ridge Associated Universities site (affiliated with ORNL)
http://www.orau.org/ptp/collection/c...cameralens.htm
Edit: Edit: from Wikepedia
Radiation Levels
Typical radiation levels can approach 1 mR/hr as measured at the lens element's surface, decreasing substantially with distance; at a distance of 3 ft. (.9 m.) the radiation level is difficult to detect over typical background levels. For reference, a typical chest x-ray consists of about about 10 mR, a round-trip cross country airline flight exposes a passenger to 5 mR, and a full set of dental x-rays exposes the patient to 10 mR to 40mR.
I generally don't lick, finger, or pulverize my lenses so I'm not too worried about it. In fact the mantels for gas lanterns have Thorium are far more radioactive and are used to calibrate Geiger counters in the field.