In the UK there is an implied restriction of 400' AGL (or 1000' with exemption) and 500M distance maximum unless you have CAA authorisation for the flight. The main thrust of that law (article 166 and its summary) is that the pilot (or his spotter if flying with goggles) "must maintain direct, unaided visual contact with the aircraft sufficient to monitor its flight path in relation to other aircraft, persons, vehicles, vessels and structures for the purpose of avoiding collisions". I flew 400m out at 200', and after about 200m out and I looked down and looked up and .... nothing. I had lost it. So how far can you guys see ? No. Really.