Neutral - thanks for the in-depth explanation - I'm anxious to try out your ME method...
As a matter of fact this is not my method
This technique was being used around for decades in different areas.
I just was not very happy with 1Dx low ISO SNR performance (as I like night/evening shooting) and when saw that ME function in 1Dx – my first thought was that this could be workaround until we get new rumored Hi-Res camera that should bring some new sensor technologies. I was tempting to buy Nikon D800 but thought that I can wait and do something with 1Dx.
Actually Multi-Exposure term is coming from old film times when in order to mix together several images you had to do multiple exposure from different frames on the same piece of photo paper.
Same functionality was main goal of introducing ME in digital cameras – and one of the application of this to catch phases of object movement in one shot - but there are also many other interesting artistic applications for that
Noise averaging using ME for improving SNR is just very useful side effect of this functionality.
And the other side effect which is also very useful - is to simulate ND filter for long exposure.
Using ME method one will be getting much cleaner images than using ND filter to reduce amount of light into camera sensor.
If both are combined together (ND filter and ME method) you can get very interesting artistic effects due to ability to have very long exposures at day time. I did not tried that yet but going to do so at some time.