Well with clouds scudding across the sky and a fair wind I did manage a shot with 400 plus two 2x converters tonight.
One of the converters is a bit like coke bottle glass so not expecting great things. Image converted to B&W to get rid of a shed load of CA.
2 pics attatched. One is full frame and the other a crop. ISO 500 at 1/100 sec, effective aperture f22.
Sassan, we did not see a Wimberly type head at the show, so for now I will take solice in the fact that at GB £499 its cost equals the value of my 400mm lens. Interesting concept from your pics though ....................... I feel a workshop job comming on if I upgrade the 400 as it only weighs 1200g, hence the counterbalance I mentioned which is to take care of the camera weight.
Don