Archived posting to the Leica Users Group, 2000/01/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]The LHSA VF article by Bill Gordon was a follow up on the findings by Dr. Cyril Blood of the British LHS. Gordons test of the half dozen Summicrons with S/Ns under 1,000,000 showed that the average front element emitted 1.5 miliroengtens and if laid front down on an unexposed piece of film, would leave a dark circle after about one week. This is far less radio- activity then the radium dial wrist-watches of the past. I dont mean the calcium disulfide luminous type but the radium dial Omegas & Rolexs. For many years, the Leitz management denied using radioactive thorium but when confronted with the actual findings, finally admitted to it, along with many more lens manufacturers, but the Leica pre-1M are the most famous and command a premium price today even though the yellowish brown tint of the lenses will discolor chrome films. Frau Doktor Mary Grace McGough In a message dated 1/27/00 2:28:04 PM Pacific Time, zeissler@wt.infi.net writes: > > According to my wife [who does radioactive particle analysis for a living], > distance would play a crucial role in whether the film was exposed or not by > the Thorium elements. According to her, the alpha particles would not > expose film outside of a fairly short distance [~2 inches or less, depending > on some variables], while gamma particles would travel several yards. >