So I just picked up the canon 17-40L f/4, and am really impressed with it. It is my first L series lens, and going from my tamron lenses its just unbelieveable as I'm sure anybody who has used one already knows. I was looking on Canon's website, and they talk about how they use manufactured flourite in their L-series line. They have a lot of literature on this flourite mainly because they say it has a low refractive index. My question is do they use this flourite in all of their L- series lenses, or are some of them outfitted with just the super UD glass?