All the Canon super telephoto lenses (300mm and up) use one fluorite element and two ED (Canon calls it UD) glass elements as well as the usual optical glasses. All the L lenses have either or both an ED element (or two) and aspheric elements depending on focal length and or zoom.
For instance the 135mm F2L has two ED (UD) elements.
The take home message is you get what you pay for.
If you shine a green laser pointer into a lens with a fluorite element there is no scatter from the fluorite element unlike the glass elements. It is almost as if it is not there.
More info here
http://www.usa.canon.com/consumer/co...categoryid=153
Bert