so i've been having a lot of fun playing around with my new Olympus Evolt E-500 (and i hope to get my first set up here soon). but i've been having trouble doing proper motion blur. i set my camera up on a tripod in front of a mirror and did some simple motions like arm flapping. but every time i'd come out all ghostly and transparent. i changed the shutter speed several times but the same result. what am i doing wrong?