Quote:
Originally Posted by Vudoo4u2
never said the extension or the 1.4tc cause distortion...(if my long winded paragraph made it sound so...it was unintentional)
I was saying that when using the 1.4TC, you must give up a stop automatically, so starting from 2.8 and going to 4, is amazing (b/c you have a ridiculous telephoto thats F4)if you started with F4, and lost a stop to F 5.6, youre pretty much giving up the ability to shoot hand held in low light without huge iso bumps @ F5.6
as far as the macro tube, it works on both 2.8 and 4 w/o giving up a stop...so theres no difference really there, but the bokeh when you do macro shots is really nice with 2.8 vs. 4
its the 1.4 TC that has the difference b/c you give up a stop 
and the F4 is not SIGNIFICANTLY sharper, its pixel picky sharper, but we'll see whos sharper when the lights go down  |
Agreed. It really isn't that much sharper at all. It's been tested over and over again and the the general consensus is that unless you're pixel peeping, the difference isn't that noticeable. There's also rumors of a new 70-200 2.8 IS coming out which should incoporate the flourite element and a newer IS system. Of course it's going to be quite a bit more than the current one so if you (OP) can afford it, you should go for the 2.8 IS now.