Originally Posted by henry link
If you want to see just how far answers to your questions can go try wading through all three pages of this thread about recent developments in ED glass for high end telescopes:
If we assume that Zeiss used Schott glass in the FL binoculars it's unlikely that the so called "FL" glass has an Abbe# any higher than about 83, since there was no glass type with a higher value in the Schott catalogue in 2004 when the FL binoculars were introduced. Schott only recently developed a true Fluorite equivalent glass, N-FK56. That one might be what Zeiss calls "Ultra FL".
That's interesting. The FL still has a great image. I know they have been updating the coatings over the years. Would upgraded coatings alone change the image from a slightly warm to a more neutral/cooler image?
Early FL's are reported to have slightly warmer tone.