I had an electric focuser lying around so with a pulley and timing belt from Radiospares I put together an electric focuser rig for the Canon 5D MkII and the 100mm macro lens that took the mega-wide-field Virgo/Coma galaxies shot. If I find there’s mileage in this approach I will invest in a prime 200mm Canon lens which has a 72mm diameter lens (and I have an IDAS filter for this lens size).
