For me to make it easy to use I just registered ME and Mirror lockup in the1Dx custom menu (last tab).
Neutral: could you please give a step by step instruction how this can be done?
This is how to do this in 1Dx:
1. Enable multi-exposure
1.1. Set ME mode to continuous .
1.2. Set number of exposures to 9 (or any between 4 an 9 - smaller number will give less SNR improvement)
1.3. Set multi-exposure control to Average (to integrate over 9 images) ,
2. (Optional) Switch on mirror lock up function with the SET button deactivation to reduce camera vibration (will be deactivated by SET button). See explanation for this in my post above
3. Switch on Long exposure NR - set it to auto - will be used for shots longer than 1 sec or set it ON -"forced" . This adds additional SNR improvements and significantly reduce banding
4. Put camera in high speed continuous shooting mode ( optional - if you are shooting in high DR daylight environment to make ME shot very fast) , press shutter - mirror will be locked, press shutter again to start ME shot and keep it pressed for each next shot in ME sequence until ME sequence is completed
Camera will take quickly 9 images in less than 1 sec (that for daylight - at night will be longer ), stops and then merge it ( integrate) into one image.
And you are done.
Now press set button to return mirror back (if mirror lock was used) and then you could see the result.
Method is suitable for only still images.
In normal (daylight) conditions such kind of shot will take about 0.75 sec with FPS =12
And of course method should be used with strong stable tripod for camera and remote shutter control (to prevent image blurring due to camera vibrations and get highest possible resolution)