I really like my Optitek mount but recently I tried to put a 1.4x Kenko teleconverter on it and it wont mount. The teleconverter is just slightly too bulky and hits the screws on the Optitek lens locking ring. Looking at photos of other types (Nikon, Sigma etc) they all look rather similar in this respect. Does anyone know of one that does work? I've never had a problem with any lens I've ever tried so it was a bit of a surprise.