Hi,
Many thanks for your comment which is truly appreciated. However, My aperture was stopped down to f8 and with 1000 and a fairly steady hand I would, from past experience with other long lenses, have expected to get a crisp shot either with or without the excellent OSD provided by Fuji.
Nevertheless I will try using a tripod to check whether that is indeed the problem.
Incidentally, I tried using the Photoshop shake reduction filter to see if that would remove the "halos", but it did not work, perhaps because the algorithm didn't recognise a shake movement?