70-200mm f/4 vs 135mm f/2

[csnudelman]

Ahhh gee, just when I was fix'in to order the 70-200mm f/4.0 I find out the AF for the 20D only works well/works better if the lens is f/2.8 or faster. The 70-200mm f/2.8 is just too big and heavy to haul around. I guess I could get the 1.4X to use with the 135mm as well. Thoughts anyone? :confused:

[drewmk2]

"the 70-200mm f/4.0 I find out the AF for the 20D only works well/works better if the lens is f/2.8 or faster" Do you mean the teleconverter only works well if the lens is f/2.8? I'm confused.

[Toogy]

I think he talking about the 20D being able to focus 'better' if the lens is a F2.8 or better by allowing more light in.
FWIW I have a 70-200 F4 with my 20D and don't notice any focusing differences whatsoever compared to my Tamron 28-75 F2.8.
Anybody else have more clarification on this?

[tommykjensen]

Have a look at this thread that deals with the same "issue"

http://photography-on-the.net/forum/showthread.php?t=75445