Its all about discretion. Keep it as a hobby and be sensible. Scanners+cameras+bins+asking for a runway view will always raise suspicion! I've been around the world and photographed in many places - Libya, India, Greece, Russia, South America, etc - and only been stopped once.... in Israel!!!! Luckily with a little foresight I had a sketch of a bird in my note book and I said that I was bird watching.... I returned to my hotel and then on to the UK! And the poster who mentioned the US..... who'd want to go to the US these days anyway? RR