"== The optical formula did not change between incarnations. == 

 I've heard this several times, but not from a definitive source;  this is why I put a cite needed tag in the article.  It makes sense that a different type of focus motor shouldn't affect the optics, and that Canon ( or anyone else ) wouldn't invest R&D; in developing a new optical formula if it isn't needed.  Between this and having been told a few times ( at a pro camera store, online ), it passes my level of ""probably true.""  Still, it needs a citation, and if anybody else feels like this doesn't pass the threshold, Wikipedia says to act bold and remove it. 

 Hopefully somebody has access to diagrams of the glass in both lenses, or can settle this somehow?   "