[Canon Ball]

Currently holding a 70-200mm f/2.8L with 40D body.
Needed to have more zoom power for taking birds photos.
With this extender I can have 400mm zoom but reduced the f-stop to f/5.6.
The extender cost around $2200. Please advise C-hing and let me know is it a good investment?

[gwu1]

I tried 1.4x on 70-200 f4L IS and 40D. Not sharp enough at wide open.

100-400 is better than the above combination.

[Canon Ball]

Finally, I found the related information.
http://www.luminous-landscape.com/reviews/lenses/400v400.shtml

[老叟]

I use this X2 extender for wildlife, not bad at all

[gwu1]

Canon Ball,

Thanks for the link. This is similar to what I have found with my 70-200 F4L and 1.4x. 100-400 is really great even at 400mm and wide open at f5.6.

see

[variosonnar]

2x doesn't work well with L zoom lenses. It's a far better match for the super tele L primes (e.g. 200 f/2, 300 f/2.8... etc)