I bought extender 2x for Canon (arrived yesterday). So far I took only 3 pictures with it. I lost autofocus so I feel like years ago with Bronika and have to practise focusing before I post something into gallery. If I manage to include a picture -see for yourself. I put it together wirth my 100-400 L IS Canon zoom, and was practising to focus on crane opposite, min 1 km away. If I can read something written there. It is not the sharpest image I have ever seen, but for the distance, not too bad. So 400*2*1.6 (for sensor) = 1280 lens.
Susan