Originally Posted by Rowdy
I have shot back to back with the 70-200 2.8 and f4L IS.. and I can tell you right now that the 4fl IS is sharper. I love that lens!
the 70-200 f/2.8 IS version 1 is supposed to be both less sharp than the non IS version and the f/4 IS versions. However f/2.8 IS II is a whole different animal. I upgraded from f/4 IS and it was totally worth it.
F/4 IS is amazingly good for the price though, and if you don't need 2.8 or want the weight of a 3 and a half pound lens, it is a solid performer.
To be fair though, I would take the 2.8 non IS over the F/4 IS just for the aperture control and the extra stops of shutter speed i'm allowed. I don't think the prices are that different.
I've just grown accustomed to needing 2.8 when im shooting in low light and flash is not allowed/appropriate (e.g. religious wedding ceremonies that prefer us not to use speedlites or strobes).