Hi, Francis, This is apparently caused due to the fact that the glass elements were made of rare earth elements, which over time decompose, depositing the decomposed material on the glass surfaces.
Over at YahooGroups Spotmatic, one of the members actually took his 1.4 to a friend's/relative's lab, and sure enough, the Geiger counter measured the lens as "hot". Not enough to be a health hazard, but measurably well above normal. I have a 1.4 50mm afflicted with the "yellow curse", and it's fine for b&w. In fact, it's a terrifically sharp lens. The yellow cast makes colour unaccepatably "warm" for me, but I don't think that the yellowing is as strong as a yellow filter for b&w work. In fact, I don't think my lens is any slower than a non-yellowed one, although I haven't had it tested. regards, frank Francis Alviar wrote: > I've read somewhere (print, on-line) that some Pentax > screwmount lens glass are turning yellow. What causes > this and which lenses are involved? And most > importantly, when the glass finally turns yellow is > the lens rendered unuseable or can I still use them > for certain applications (B&W maybe)? > > Thanks. > > Francis M. Alviar > Irvine, CA > Sign up for SBC Yahoo! Dial - First Month Free > http://sbc.yahoo.com > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . -- "The optimist thinks this is the best of all possible worlds. The pessimist fears it is true." -J. Robert Oppenheimer - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
