[davidmanze]

Canon has used fluorite in tele lenses since the 1970's. The two purple elements are fluorite. Nikon has, for decades, touted that thei "ED" glass was superior... until they finally were able to use fluorite element. Their FL lenses use fluorite in a similar way as Canon does.

https://imaging.nikon.com/lineup/lens/f-...ic_003.jpg

Canon:
http://allphotolenses.com/public/files/o...18c337.gif

Thanks for that BC !! 
 
 I remember the Nikon had a double fluorite front elements .... the Canon has a similar arrangement then?

   Quite a weight saving on the Canon!

  What were the lenses that Klaus linked with only one front element then? I don't have a translate on my browser ...... and I don't read hieroglyphics