#4. "RE: How'd I screw up? Exposures off as zoom in" In response to In response to 3
Make sure the lens is stopping down when set to the 70mm position. I would set the camera on a tripod or any surface where you can look into the lens during a long exposure and see if it stops down to something like f11 or f16. Or if it stays open to f2.8 when it shouldn't.