I read an army report which covers all the major lens makers and their lens coating technology. Report writes that Leitz Wetzlar was using a low quality East German lens coating device and only positive side , it was very sturdy.

Last night I was reading an other report and it was telling the coating thickness difference at an highly curved lens.Book was about sol gel processes and I was reading about the nonlinear glass making technologies.

Leitz Wetzlar was using two materials to coat their lenses,

MgF and ThF4. There is a large knowledge collection on these materials on wiki or commercial companies. Leitz director reports they want to change from ThF4 to YtF?. I think these were the years that start of radioactive materials use tightly controlled or banned.

Report tells all Leitz coating materials been bought from MERCK.

May be some japanese companies used thorium at their coatings and sold their lenses as thorium glass. I saw some Pentax comparisons and thorium one have less flare , stronger blacks and colors but overally they cant be compared with Leica.

Mustafa Umut Sarac
Istanbul