[Retrograde (Pete)]

I looked into buying one of the Pentax 6x7 Thorium lenses (the 105mm f2.4 I think).
The old Thorium lenses can often be identified by the yellowish appearance of the glass I believe. I decided against it as I thought the yellowing probably wouldn't be ideal for image quality and would only increase with age (one of the examples I saw on ebay showed a significant yellow appearance of the glass). I doubt the radiation given off is significant enough to be any sort of health worry (unless you store it underneath your mattress or something).