70-200 f/2.8L or 100-400L

[agsurfer]

I have been shooting with my 17-85 EF-S lens on my 20D for a while and I am ready to make an investment in another lens. I am interested in the 70-200 mm f/2.8L IS and the 2xII T-con. The other logical option would be the 100-400 mm L IS lens. Pros/Cons? Any suggestions?

[grego]

I have the 70-200mm f/2.8L IS + Canon's 2x Extender.

I have loved the combo. As a photo jounralist, I need the fast lens, but for outdoor sports, I can get away with the f/5.6(with extender on) because of the sunlight.The biggest con, is that it's 5.6 when on. With the conversion factor(1.6) and the 2x, you essentially get up to 640mm. And it's pretty damn fast, still with the extender on it.

Here's a sample of what it can do. http://img.photobucket.com/albums/v357/greg9683/MyPhotography/CRW_6600.jpg

[RbrtPtikLeoSeny]

Question is how often you'll be using that T-con on the lens. If your going to be shooting a whole bunch of stuff at 200mm plus most of the time I'd suggest you get the 100-400L, because with a 2x t-con your going to lose a whole lot of image quality. If your shooting a lot of indoor, or close up stuff, then I guess the 70-200 plus t-con combo would be a good idea.... still.... 2x t-con? 1.4x would keep the lens a lot faster, and a lot sharper.

I donno, ideally it'd be good to get both, but that's a lot of $$$$....... so, it comes down to what you need. More on the very long end? Or more on the very short end? Because long end your going to lose image quality with the 70-200 t-con combo, and on the short end your going to lose apeture speed and auto focus speed with the 100-400L.......