I was slow to learn that my 800mm lens will autofocus with a 2x extender on, but only in Live view mode. I was in a hide with Nick Martin and he borrowed my 800mm for a distant Osprey shot. The next thing I knew he was auto focusing with the 2x on while I am telling him he can’t do that, it does not work. But it appears it does and the rest of the world knew it, but not me.
In live view the focus system works on contrast rather than “phase” focusing and it is slow, but it gets there. Nick feels it is best to zoom in the live view image to get the result sharp. It certainly works. Taken on a focus4nature tour in Finland.
Canon 800mm and 2 x extender. Canon EOS 1d Mk1V. 800 iso. 1/1000th at F16. From a hide by nest. With the cameras built in 1.3 crop that is a 2080mm lens. I always imagined we would start to suffer with heat haze at such magnifications, but no sign of it.