I bought a Teleconverter Tamron-F for my sister's Sony alfa300. I paid it really a few euros, because it was in the box of the not working pieces. But the lenses were perfects so I decided to take it and try at home. When I tried it on the camera I've seen it doesn't transmit the autofocus at the lens. I had thought the problem was in the gears inside the converter, but they were perfect. So I measured the little AF iron tooth on the camera and the groove in the converter and I found they were exactly of the same dimension (1,3 mm) so it's not strange that the tooth doesn't fix in the groove. So I decided to enlarge a little the groove. I show you how to do that.