Kin, could you give us your impression of the IQ at 600mm?
Also, could you give us your impression of the IQ at 400mm compared with your Canon 400/5.6L, either that or perhaps post some comparison pics?
The 400/5.6L is unbeatable for sharpness and AF speed, at half the weight. The big problem is that ludicrous 3.5m minimum focus distance. The 400/5.6L that my wife uses is very sharp.
With care, the 600mm @ f8 is fine. We spent a few days at Long Point, and it was great for tree top warblers in good light. But in the dark canopy and cloudy days, I switched back to my 300/4L IS + 1.4X for the weight, and ability to shoot wide open and AF speed thru the branches.
