Originally posted by denik Leica uses a cement between elements they call 'absorban"
I have known about absorban for quite a while, It has been mentioned in the Leica M Lens compendium (2001 Edition) but it is the first time I have heard the claim that it attenuates UV at a greater rate than glass itself. they would have to use a lot of it in their lenses* to accomplish this degree of efficiency. The funny thing is that I own a Leica branded UVa filter. However it is probably counterfeit, as Leica staunchly held the position that all filters degrade image quality by introducing spherical aberration, regardless of how thin they were.
* Over many years of restorations and repairs to Leica lenses I have been using standard UV curing cements without issue, imaging characteristics of the restored lenses are basically identical to copies already in my possession.