I only recently looked through my first USO. I was impressed and believe there is an appreciable difference between it and my $1100 MKIV (which I dearly love, and believe is in excellent optic for the money). I have not looked through an S&B. My question pertains to the differences between USO glass and S&B glass, as well as some on the other top German glass makers. Does USO use proprietary glass, or is it sourced? I seem to recall reading something about Schotts or something similar, as being a maker of high end optical glass, but searches have not turned up much. Just trying to understand who makes what and why some of it is superior to others. Where can I go to read about this topic specifically?