回复：这是俺20美金的架子在沙漠地上长爆三十分钟拍的。 (图)

The camera shake must be due to two reasons:

1. Cars driving by. I was only 5 feet away from passing cars, so the wind and ground vibration will affect the camera.

2. I shifted my weight.

For your 30min exposure, you can walk away so that during most of the exposure time, there is nothing near the camera (no wind, no vibration from the ground).