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- Gavin
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I've just bought a 2x extender to go with my 100-400L lens 
I had read before hand that the AF doesn't work on anything but the top-end camera's.
I'm using a 450D with the above set up.
I had resigned myself to 'learning' to manual focus all the time, which @ 800mm is not especially easy, especially since I was hand-held trying to capture birds!
Anyway, I'm not sure if it's widely known, or in fact, if it's known at all, but you can use the AF with the extenders
You just have to use it through the live view. I had switched to live view to get the 5x and 10x mag so I could manually focus better, and thought I'd just try the AF button... lo and behold, it only bloody worked!! Am seriously chuffed with this new knowledge.
If going for a static item or a fixed focus point, you can use the live view to set the focussing, then switch back to viewfinder should you so wish.
I took this pic below using the live-view AF (it's through a window so it's not the best, but I'm quite chuffed with it considering).
I had read before hand that the AF doesn't work on anything but the top-end camera's.
I'm using a 450D with the above set up.
I had resigned myself to 'learning' to manual focus all the time, which @ 800mm is not especially easy, especially since I was hand-held trying to capture birds!
Anyway, I'm not sure if it's widely known, or in fact, if it's known at all, but you can use the AF with the extenders
You just have to use it through the live view. I had switched to live view to get the 5x and 10x mag so I could manually focus better, and thought I'd just try the AF button... lo and behold, it only bloody worked!! Am seriously chuffed with this new knowledge.
If going for a static item or a fixed focus point, you can use the live view to set the focussing, then switch back to viewfinder should you so wish.
I took this pic below using the live-view AF (it's through a window so it's not the best, but I'm quite chuffed with it considering).