Originally Posted by
Junker
I am no pro, but here are my thoughts. Mirror lockup is good for long exposures with in reason-like 1/15, 1 sec, 10 sec, 30 sec etc. There is a point where your shutter speeds become so long (and as a result, very little light is striking the sensor i.e. F/22, or it's sensitivity is very low i.e. ISO 100) that a slight shake changing the placement of light on the sensor has no noticable effect- for exposures >2 minutes doesn't seem to matter. THough it's probably a good habit to form by using it.