After much debate, viewing of image samples, reading stats and reviews I am adding a Sigma 500 f/4.5 APO EX HSM to my arsenal. I think I'll end up with a pretty versatile kit between the 70-200 and 300, both 2.8 APO EX DG HSM's, the 500 and the 1.4x & 2.0 TC's. I am very happy with the results I get with 300/1.4x combo, and the 300/2.0x combo is totally acceptable but I am lusting for a 500 prime. The Nikon 200-400 VR and the 500 have a third of a stop advantage, and Nikor glass, VR, but the Sigma is a fraction of the price and the copy I am buying is a pristine pre-owned lens. Plus, I think it will be easily sold if I decide to make a change in the future. Here's my question.. I would expect the 500 + 1.4x TC to defeat AF. Sigma claims it does, and a few posts I have come across support this. I would like to use this combination anyway and having a Katz Eye in both bodies should be a big help. I have read that taping one of the contacts on either the lens or TC allows it AF regardless, but can't find any details on which contact to tape or how exactly the tape should be applied. Can anyone help with details on how to do this??