Thanks Martin, I see you have already answered some of my asks, lucky you!! the lens you are using is on my wish list now I know why your shots are so sharp plus a good steady bean bag which I know should make a big difference.
I have not been into photography all that long only used a point and shoot but moved up to DSLR to try my hand at photographing birds, lots more involved with a medium format camera than first thought. I use a Canon eos 1000d and the lens I use for birding is the Sigma canon fit 170-500mm f5-6.3 APO DG but finding I wont get the photograph results I want unless I move on to a lens similar to your own that's my thoughts anyway.
Hope to speak again soon and I will watch for anything new in your
Gallery.. Regards John.