According to Olympus the MC14 is compatible with only the 40-150 PRO and 300/2.8 PRO lenses. I'm wondering if that restriction is based purely on mechanical reasons, i.e. the MC14 lens elements protrude beyond the bayonet mount, and will touch the rear elements of any other lens in the m4/3 lineup. And therefore, if so, could you not attach a smart adapter, 4/3 to m4/3, to the MC14, and use any 4/3 lens, complete with AF etc ? And similarly, why not a dumb adapter to any legacy lens ? The reason for this thought train is that I also suspect the best teleconverter optics would be when the TC lens elements are closest to the camera sensor. Along that line, consider the Metabones focal reducers. Their optics are at the camera-end of the focal reducer, and just the gap at the lens-end varies for different brands of lenses.