The Canon 500 f/4.5 L is a very sharp lens but it has two challenges – no image stabilization and a f/4.5 – which is fast but with the 1.4 TC is f/6.7 – which is shy of the required f/5.6 that most SLR’s need for auto-focus. Although the 1D series cameras will still autofocus off its center point - I never had a 1D camera with this lens so my 700mm shots were manual focus. Besides those qualifiers this is a super telephoto, it focuses very fast (I believe as fast as my 500 f/4) and its light 6.6 lbs makes it very manageable. Therefore if you shoot from a tripod and have live-view for using extenders then the 500 f4.5 may fit all your needs. However, if you shoot in vehicles or need autofocus for use of extenders then the 500 f/4 will be a better option.

My 500 f/4.5 was stolen in 2003 and replaced by the 500 f/4 IS.