Originally posted by Blue However, it was one of the earlier versions of the Super Tak 50/1.4 that had thorium and not many other Taks did.
Huh? It was my understanding that most of the ST 50/1.4 (particularly later copies) were thoriated along with all S-M-C/SMC Takumar 50/1.4.
That being said, it had been my understanding that Pentax ceased production of lenses with thoriated glass with the K-series. The link in the comment above seems to indicate that this is not correct.
For general interest, here is a link that I have posted in the past showing relative radioactivity (both counts and gamma intensity) for multiple lenses from the late 1960s through the mid-1970s.
http://www.flickr.com/photos/s58y/6802092736/
Steve
(...only owns one "hot" lens, an Auto-Rikenon 55/1.4 and yes, it is yellowed...)