Quote Originally Posted by jsimoespedro View Post
Thanks for the replies. So to summarize:

1) If on a tripod, always use mirror lock-up.
2) If not on a tripod, forget it. Holding the camera steady is more important.
Yes, this. However in terms of rule-of-thumb for (2), I find that the usual t=1/f rule gives acceptable sharpness, so I tend to shoot 1/125 with my 110mm lens and 1/250 with my 180 and 250mm lenses.

People vary a lot (like a factor of 4) in their shakiness and cameras vary in the mirror weight. For sure you can shoot at slower speed with a rangefinder than a big SLR, and probably slower with a 645 than a 67. Having a long heavy lens on the camera will damp the vibrations significantly due to its moment of inertia.

With tripod and MLU, I try to go no slower than 1/15 on portraits just for subject-motion reasons. Your hit rate at that speed is not 100%, but there will be a good fraction of shots that are razor sharp.