thanks jo-anne,and paul.
skyviewer: the 100-400 is a very good lens.i just sold mine.the best zoo lens! unfortunately,hand-held,the 40-d/500 mm, combo,is not a very good flight shot duo, for me at least,due to the heavy weight,and long focal lenght,which makes acquiring,and tracking your subject, very difficult.i,ve been experimenting with a 300 f/4 + 1.4x extender,and had some sucess,yesterday with geese.much easier to lock focus,and track,beeing much lighter,and affording a much wider field of view.
denis