I am still consdering getting a 55mm 1.8 takumar but i am still paranoid about the radiation. It would be best for me to try and avoid a radioactive version for my peace of mind. Anyways, is there a way to know if the lenses are radioactive. The one i am looking at getting starts with 153 in the serial. And the glass looks yellow, but just on the front, so it might just be the coating. Anyways i was looking on pentax forums here: http://www.pentaxforums.com/lensreviews/SMC-S-M-C-Super-Auto-Takumar-55mm-F1.8.html I took this directly from the page. It says " From the 1965 version, at least one of the glass elements is made from radioactive glass" They then tell you how you can differentiate the two: "1962: Super-Takumar 1:1.8/55 (first version) - fine knurls on aperture ring 1965: Super-Takumar 1:1.8/55 (second version) - coarse knurls on aperture ring" So if i am understanding this correctly, only the second version out of these two has radioative glass. Anyways, how can i tell if the lens is the first version or second one. It mentions the knurls of the aperture ring but i am not sure how much of a difference in size they are. Anyways, does anyone know if this version of the lens is radioactive? I have a picture of the lens i was planning on getting here: https://flic.kr/p/vJhAcb Thanks in advance.