And the f/2.8 lenses come supplied with a tripod collar, but it's an extra cost (v high) accessory on the f/4 lenses.
I got a cheapy copy off Amazon but the tripod thread looked very fragile so I had to drill it out and put a bolt through.
I bought mine from this site:
http://www.foto-tip.pl/sklep/canon_tripod_mount_ring_66mm_equivalent-p-1282.html
Just don't expect it to be similar to Canon Quality, but it dose the job ok, at list the colour matches the Canon standard.
Is it sturdy though?