The hat method
Using the "hat method" you can avoid oscillations of the tripod and the attached telescope caused by the movement of mirror in the reflex camera. First you set the exposure time of the camera to "B" (arbitrarily long exposure). Then you cover the objective of your telescope by a large hat. After opening the lens shutter with a remote release-trigger, you have to wait several seconds until the oscillations have relaxed. Subsequently, you release and cover again the objective for the necessary exposure time by the hat and finally close shutter.