Lead Glass and Lead-free Glass for Photographic Lenses

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