I'd agree with Phil - for widefield, you really want between 15 and 50mm - not 100mm or 200mm.
Star trails look best when there's some foreground interest/scene. At 200mm, you won't get anything in the foreground.
Mine aren't nearly as good as Phil's, but this
Southern Cross and Eta Carinae was at 35mm, and this
Scorpius one was at 24mm.