Xti with 400 5.6, which TC to use to retain AF? (1 Viewer)

Hi all i recently acquired a brand new 400 5.6 and I'm very happy with it but i would like to stack on a 1.4x TC and see if i can maintain AF.
I've read that the Tamron 1.4x does this so i picked one up at a discounted price of a camera forum and it doesn't even work at all.
Everytime i take a picture it tells me there is an error communicating between the lens and the camera and it says to clean to contacts.
Now i'd still like to use the TC even if its only in MF but i can't even get the TC to work in the first place.
Any advice is appreciated, thank you.

hi i use the kenko 1.4 with my 400 you have to tape the pins to get af to work

it has been discussed a few times on this forum if you are not sure what taping the pins mean

The Kenko 1.4x should work as does the Canon 1.4x but as mav12 says, you need to put tape over the pins. PVC electrical insulation tape will do. As you look down into the lens end of the converter with the pins at 12 o'clock it's the three left pins that need tape placing over them and then fit the lens.

Using tape in this fashion means the presence of teleconverter isn't reported to the camera.

However autofucs will be noticably slower and may hunt a little.

An alternative would be the Kenko 1.5x MC converter which has fewer pins.