This was an experiment. I used the 1.4x teleconverter and two EF12 extension tubes on the 300mm lens.
This allowed me to focus at about 5'. I tried several camera settings and was surprised that f8 worked this well.
Still, this is not going to be my macro setup. I will say though, that at regular mfd of about 7' with the 2x tv, this lens has given me some great close-ups.