Meleica said:
Brian Sweeney said:The Radioactive Summicron used Thorium in the Front Element! Most Hot Lenses used Thorium for the inner elements.
Brian Sweeney said:DO not lick your fingers after cleaning it.
Meleica said:Yellowing glass is from "radioactive" lens elements and their decay. This is not dangerous unless it is constantly kept close to your eyes. Many lenses from the 60's to 70's used these glass elements ( many with thorium elements ), including Leica, Canon ( 50/1.4, 35/2 ) and Pentax Super Takumars to name a few. To get rid of the yellow, follow this procedure:
you can "clear" yellowed radioactive glass by sitting them in direct sunlight for about a week. wrap the lens in aluminum foil to minimize heating, leaving the glass exposed, and set it on a windowsill in the sun. Word has it that if the problem was radioactive yellowing, it will be clear as new in a week.
The lens should be placed outside, because window glass filters out UV part of spectrum (that does the healing). Most likely you are aware of that already, just that it might be the cause in some cases.colyn said:I tried this with my 28mm SI lens but the yellow did not go away.
varjag said:The lens should be placed outside, because window glass filters out UV part of spectrum (that does the healing). Most likely you are aware of that already, just that it might be the cause in some cases.
Brian Sweeney said:How about going with just "Summicron" rather than "Summicron-M"?
http://flickr.com/photos/pictures_with_old_cameras/269321604/