Not scientific, hardly controlled (shooting through my laundry room window glass), but fun nonetheless. I'd posted a few weeks ago that I'd bought two of Oly's old converter lenses at a pawn shop for $10. $35 in step up/down rings, and here it is mounted on my E-M1. First shot is Oly 40-150R maxed out to 150mm, second shot is same lens at 150mm WITH Oly B-300 converter attached. Sharpness really suffered, but this was handheld AND through a glass pane, so don't judge too harshly (me or the lens!).