May I offer an update re the 2.0x teleconverter. It is stated in the excellent lens summary above that you lose phased contrast detection when coupled with the 50-140mm lens. Actually - it does keep contrast and phase detection. You do lose phase detection with the 100 - 400mm tele when coupled with the 2.0x because it cannot get enough light through. I have successfully taken high speed focusing shots in low light with the 50-140mm with the 2.0x converter so I thought I'd give this update. Also more here: https://www.digitaltrends.com/photography/2x-fujifilm-teleconverter-announcement/