Quote Originally Posted by HDNitehawk View Post
In and of itself it is just how the lens is constructed. The IS version is an L lens, so theoretically much more went in to its design. Really it doesn't tell you it will have better or worse IQ because a lens with the same elements and groups could be improperly made or designed.

Not to make sellers remorse for you, but yes the IQ of the 100mm IS L is better than the 100mm non L's. The L version is a newer lens, and has the new coatings Canon started putting on lenses with the release of the 24L II. The charts show the L version to be better, and the ISO charts show it to be better.

Keep this in mind though; in the real world the difference in IQ is very fractional. Only when you pixel peep the fine detail would you probably notice.

As for your loss of IS, do you still have your macro flash? You could still chase the very small critters.
Well, the latest upate on my macro lens issue is that I received the Sigma 70mm yesterday and am returning it today. It didn't focus as well as the copy I had before and it was the old Sigma finish (ewwww) so I am still in need of a macro lens! And, I am still really torn on my decision of whether to get yet another 70mm or a different macro all together. I see Canon refurb's site has the 100mm non-L, non-IS lens in stock but I do not still have my macro flash and I guess I am worried about what was mentioned that the IQ is not as good. I'm sorry for being so indecisive on this but once you've gone "L" it is really, really hard to downgrade and accept the downgrade without constantly being critical of the results from the non-L, non-Canon consolation prize.