A couple of nights ago while staying with a friend in Tauranga I had a chance to take a series of shots of a ship leaving port from a hilltop home.
We could just see by eye a large container ship leaving port. From where we were sitting it was estimated that the ship was approx 20 kms from us. In the first shot you can see other homes around us. In the second shot taken at 80mm equivalent you can see the sports center across the estuary from us. About 6 kms in a straight line. The final shot is at full zoom and the ship is easily seen.
Note: The second and third shots are taken directly from camera.