This Red-crested Pochard fell into my "trap", which is a little trick I use when possible, being much too lazy for bird hides and such. I simply try to get the low sun in my back and sit very still. That way birds in the water see only my silhouette and get fooled now and then. When they see through my trickery they are usually quickly gone.
Another advantage of this strategy, is that the light is of course fully on the bird, and with the setting or rising sun, that is not a bad thing...
The 500PF by the way, does really well in strong light, a step up for sure from the 400DOII+1.4TC which prefers more gentle light. I am afraid my Canon stuff is gathering dust at the moment.
I understand about gathering dust, but I've been reacquiring a few EOS lenses of late for my Fuji system. They work a charm via the Fringer II adapter, many many of them except the 400DOii if you can believe that
But my 400/5.6 and the EOS 100400ii work fine.

Even with the 1DX2 + 600, I couldn't get in the right spot to land a nice Phoebe shot. 









