Here's another thought. It is generally accepted that the range of shutter speeds that may compromise IQ due to mirror vibration (and/or shutter vibration) is from 1/30 to 1/2 second or thereabouts. IQ doesn't seem to suffer at speeds greater than 1 second. Consider using a neutral density filter to attain slower speeds to reach 1 to 2 second exposures. This, however, may be counter-productive if wind-induced vibration is a concern, though even without an ND filter the wind would likely cause some level of vibration. Of course anything else in motion may also be blurred, e.g. foliage, clouds, etc.