The yellowing of some of the old lenses is caused by the radiation of the slightly radioactive materials (like thorium glass) which are used to make these lenses. I would not worry about the radiation but about the color shift on the pictures made with the lens. Some have said it is the lens cement which yellows... but I believe it is the lens glass itself which changes color. I remember reading that diamonds are sometimes colored with radiation as well...
You'll find a lot of info about this if you do a net search (for example "pentax radioactive yellowing"). Antti-Pekka --- * Antti-Pekka Virjonen * Fiskarsinkatu 7 D * GSM: +358 500 789 753 * * Computec Oy Turku * FIN-20750 Turku Finland * Fax: +358 10 264 0777 *
