Many thanks for all the replies and helpful advice - the area we are photgraphing is huge and straightline distance will be about 1600NM, we require quite high resolution to be able to see ground features quite clearly (hence why I am quite keen on the Sony Nex7) and understand what some of you have said about edge-blurring, which leads to another question - is there a calculation for the shutter speed for a given TAS?? or is something like the Nex7 clever enough to be able to avoid such problems. What we may do is get a Hero3 as backup and take video on HD then take still from that - any thoughts?