Larry McGarity , Dec 14, 2004; 09:11 a.m.
I'm guessing this question has been asked a couple of hundred times in this forum. There many many threads on it in the archives.
If you are buying a third party adapter $200 is a rip off. Adorama has one for $39. It looks to have no glass and you lose infinity focus. Hama makes one with glass that runs around $100. This degrades your image a great deal and the quality of your photographs will not be high.
If you have long telephotos you might try to find an original Canon adapter. It acts as a 1.26 teleconverter but preserves optical quality. It can only physically mate with a select few lenses and the last I saw went for more like $400 to $500.