that's why you sometimes need to 'cheat' 5 stacked two second images are the same as a ten second exposure in terms of time. Stacking them using layers in photoshop alllows you to remove blurred areas if they are a problem - them image I posted earlier was effectively an 8 second exposure - there's no unwanted blur but using 'lighten' in the layer properties means the stuff like light trails blend together.
