Archived posting to the Leica Users Group, 1999/08/01
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Ed, I call your attention to an article in the LHSA Viewfinder 29/3, third quarter 1996. In an article on the early 50/2 Summicrons, Bill Gordon wrote a well researched article about the use of thorium oxide glass in these lenses. Bill reports low but measurable levels of radiation from these lenses as tested by a Geiger counter. He also cites an earlier report by Dr. Cyril Blood in the Leica Historical Society Newsletter on the use of thorium oxide by Leitz in the Summitar* and early Summicron lenses. According to Bill, Leitz never officially acknowledged the use of these radioactive elements. This is understandable in that they would not want to alarm employees or users of the radioactive elements in these lenses. Many other manufacturers of optical lenses also used this radioactive glass. If radioactive thorium oxide was not used in the early Summicrons, how do you explain the positive readings obtained with a Geiger counter? Bill Rosauer