I have a question related to exposure duration and motion blur. I would think that once the exposure duration is beyond 1 second or so (probably even shorter) any motion blur due to tripod vibration would be more or less equivalent, on up to 30 second exposures. In other words, I don't think cutting exposure time from 30 seconds down to 5 seconds would really make a difference, assuming the vibration is of the same amplitude and is present during the entire exposure in both cases. In fact, during a 30 second exposure, a minor, momentary jolt to the camera (e.g., mirror slap) would probably influence the final photograph less than the same jolt during a 5 second exposure, because in the longer exposure the duration of the jolt-induced movement would affect a comparatively smaller proportion of the total light used to make the exposure. Does this make any sense? If anyone can offer any further insight, please feel free to discuss.