Calling all technical boffins . .
Had the chance to use my new Kenko x1.4 Tele yesterday.
It was real hit or miss affair with the AF on the Sigma 70-200 f/2.8.
Had constant hunting.
Tried it on the Nikon 18-105 VR this morning, same issue but not nearly as bad as on the Sigma.
Tried all different aperture stops but made no difference.
Am I missing something?
Any ideas Folks?