Originally Posted by UdubBadger
ah, ok. That makes a bit more sense. So I will need to at least swap f/4 for a 2.8 to get the f/5.6 with the 2x.
or i can just keep the f/4 and get the 100-400.
i found one article a long time ago that said the 100-400 was sharper then the 2.8 with a 2xTC attached. but i only came across that once.
the range of the 100-400 is nice to have. although the 70-200 really isn't far off with the 2x. it's really a matter of choice. I just recommend that if you do go for the 2.8 and a 2x, you'll have to stop down a few just to get the outside edges sharper, where the 100-400, the 5.6 is fairly sharp all the way across. which really is a downfall to the TCs.
hope that made sense, it seems like i jumped around a bit to me.