Originally Posted by DARK_M3
I thought about the f/4L IS. My only concern is that since I use a 50D as opposed to say, the 5D MkIII, will it be a wise choice given the limited ISO performance as noted by dcstep? In other words, will I need the faster f/2.8 mated up with my current bodies?
The f/4L IS worked fine on my 20D. It works great on the 5D2, and of course the 5D3. Is the f/2.8 better? I think the Mark II version of it might be by a hare. But, it costs and weighs twice as much. All my lenses, except the 50mm f/1.8, were f/4 when I used the 20D.
You don't need
a f/2.8 with better bodies. You need
f/2.8 if you're shooting in low-light a lot, or if you need something fast. For example, f/2.8 might be useful for weddings, but not necessary if shooting landscapes during the day.
In regards to telephoto zooms, the 70-200mm f/4L IS is probably the best bang for the buck.