I agree that these are long reads but really interesting:
http://optics.org/indepth/2/7/3
http://rohs.exemptions.oeko.info/fileadmin/user_upload/Stakeholder_comments/Exemption_13_several_industry-stakeholders_27_March_2008.pdf
Via: http://www.dpreview.com/forums/post/52159193
In short, lead-containing glass is still better optically, less temperature sensitive, more stable and actually cheaper to make. The use of lead in some optical appliances is actually exempted by RoHS directive but the adoption of lead-free glass in photographic lenses is yet the trend and the future of the industry.
Btw, I am glad that I still have some of those toxic Pentax glass that are lead-made, including some of the best F, F*, FA* and FA Limited lenses, which are now used on my Canon 5D3 FF, examples here and here! :-D
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Monday, September 16, 2013
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Comments by IntenseDebate
Lead Glass and Lead-free Glass for Photographic Lenses
2013-09-16T18:12:00+08:00
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John · 599 weeks ago
John · 599 weeks ago
Zobing · 599 weeks ago
6BQ5 · 599 weeks ago
RicardoRei · 599 weeks ago
Regards
Mike Kawasaki · 599 weeks ago
Uncle Vova · 599 weeks ago
Yes, we may agree that the old lead-containing lenses, that had been produced many years ago, is optically better then the modern lead-free lenses. So what? Should we start to seek for those old lenses immediately and use them instead of the modern lenses?
By the way, some of the aged people say that generally an old times were better in many aspects then the modern time, and they remember:
in the old days the water was even wetter then today. ;)
So what? ;) Should we seek for the well-spring of old extremely wet water to quench our thirst? ;)
RJR · 462 weeks ago
Waiting for your impressions...I have the K7 and to me is taking the K1 or leaving Pentax system and sell the FA's * 85, 80-200 and the FA 31 limited...let's see the reviews