Hmm, it doesn't match anything on the list at http://www.suaudeau.eu/memo/pratique..._centraux.html. I don't know if that's good news or bad news; if the mounting was an unusual custom arrangement, that might reduce the chances of a "partial match" (like having the right threads but the wrong spacing).

As an aside, I just love the French word "obturateur" for "shutter"; because of the cognate with English "obdurate", it suggests to me not a properly working shutter, but a shutter that's stuck closed!

-NT