I wasn't aware that Canon used flourite elements. You learn something new every day. Nice. Their telephoto lenses also use holographic elements, and I attended a talk (1990 ish) where one of their lens designers spoke about a clever scheme using diffraction order pairs (n and n + 1) to compensate each other. This allowed them to use diffractive dispersion in addition to glass (and now I know flourite) for color correction without introducing stray light (ghosts) due to unwanted diffraction orders, which are nearly impossible to get rid of. These lenses are works of art.