What you say is true, though it depends on your focal length to a degree, as well as the stability of your tripod and tripod-head. It certainly doesn’t hurt to use mirror lockup in long exposures, as well a cable or remote release, and that initial shake can introduce a softness, like a feathering effect around the sharp core of the subjects in the image.

Without a good reason not to use mirror-lockup, I still prefer to turn it on, for the sharpest possible images. It’s all personal preference though.

The best thing to do is to run your own tests (other readers). Shoot a few shots with mirror-lockup on, and a few without, making a note of the image numbers as you do. If you find it makes no difference, you could turn it off. Whatever works for you.

Good point to raise Jamie!

Cheers,
Martin.

During a long exposure, say > 20 secs, the fraction of light entering the camera during the mirror movement is tiny compared to the light entering during the stable period. For shorter exposures, yeah it might make a difference but in most cases I doubt you’d see a difference even when pixel-peeping. I think this is a case of solution to a theoretical problem rather than a practical one.

I’m much more convinced about using a remote release since it keeps your hands away from the camera and makes it easily to hold the shutter down for a bulb exposure.