im just trying to find out what shutter speeds with what focal lengths its worth using it for, which i guess ill have to just individually test for each of my lenses and different shutter speeds, as everything im reading or hearing is just contradicting each other! but so far with my 85 and below focal lengths it seems irrelevant for any shutter speed.
Camera shake, whether due to handholding or mirror slap, causes some amount of physical motion of the image sensor relative to the scene, resulting in angular blur. Whether or not that blur can be perceived depends of the amount of angular motion relative to the angle of view. That's the basis of the 1/focal length guideline (and why the crop factor must be applied to that estimate). Since the amplitude of mirror slap is fixed, the narrower the AoV (longer focal length), the more pronounced the effect, and vice versa. Other factors, like tripod stability and damping capability, play a role.
From a practical standpoint, MLU may help and may not, but it will never hurt. So, time permitting there's no real reason not to use it (except maybe battery life, not a concern for me, at least).
As stated, Live View is an even better option.
