Found it! I finally remembered where I put it! I took my Sigma 70-210mm out of its soft case, and put it in a sling bag, and put my Tamron 70-300mm USD with the 1.7 TC mounted on it into the Sigma case. Having just moved my man-cave from the 'annexe' (there's posh for you - it's actual the old stables) to the house, I can't find half my stuff! The TC is definitely 8 pin, so thanks for that, but annoyingly it is not chipped, just pass-through. This helped with the Tamron, as the camera didn't know it was being lied to about the aperture, and as there is lots of light out here, it could focus. As an addendum, I hardly ever use the Tamron, despite it being optically excellent, as the zoom ring is at the front of the lens, where I far prefer to have it at the base of the lens. With all my other zooms I can rest the battery grip on the heel of my left hand and zoom with thumb and forefinger. Taking the hand away from the camera to reach the zoom ring is just asking for camera shake - or a lost shot. I use my cheaper Sony equivalent instead. What I would really like is a chipped 1.4x with both 8 pins and screw drive, but can't find one. I have a five pin Sigma but it's a bit old and rattles!