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.
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This is the tooth on the camera body:
And here you can see the groove on the Teleconverter (already enlarged):
You need these two tools, a little screwdriver and a little file:
You have to unscrew the four screws of the back-side (side of the camera body) of the teleconverter, and also the little screws that fix the gears inside.
When you have on your hand the little piece gear+groove you had to hold it strong with some tool. WARNING! You have to be careful to not breake the nylon gear, so use a piece of rubber between the tool and the gear.
Now with the little file work on the groove to enlarge it a little. Not so much, so after a little of work go try if it fix the camera tooth. When you see they can fix with no problem you only have to remount everything (little gear first, higher gear second, metal plate third, make sure the hole in the plate is perfectly aligned with the little gear axis).
You'll see now everything works! :-) I hope to have been helpful.
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