I believe "traditionally", extenders were compatible with most white lenses, but I don't recall a black EF lens that could use them. Now that we're in the RF zone, I suppose all bets are off.I currently use the RF 24-105 f4L and have been looking at the RF70-200mm but the price is eye watering. I've never used a teleconverter and wondered if the 2x converter would work with my current lens? Seems a better option than paying nearly £2700 for the 70-200mm. Anyone familiar with using teleconverters? I Know I might lose a stop or two and hopefully the new announced converters will be compatible.