Posted 04 August 2017 - 06:11 AM
Yes a m4/3 lens would sit a bit less than 2mm in front of a C mount, but that's very little material to make the mount out of and the lens couldn't protrude past the mount because the C mount behind is so much smaller.
If you've used a 12mm lens on a 16mm camera before, the m4/3 12mm will look exactly the same. 12mm is mildly wide angle on a 16mm camera. On a larger format, any 12mm lens that can cover it will have a wider field of view, but it's still a 12mm lens. On APS-C or S35 cameras a 12mm lens is very wide angle.
If you mean "what focal length will I need to use on a 16mm camera to get the same field of view as a 12mm on an APS-C camera", then the answer is something like a 6mm lens. Or conversely, to get the same view a 12mm lens gives you on a 16mm camera, you need to use something like a 24mm lens on an APS-C camera.