kezeka wrote:
I would call into question the AF accuracy complaint when it comes to extenders since there are no motors within the extender. Clearly, I am no lens designer and do not know how extenders impact the AF calculations but it would seem to me that they would not modify the AF motor in the lens' ability to focus nor the cameras ability to convey that information. There is a possibility that the electronic connection between lens and body could be bad but I believe that extenders literally just connect the leads from the body to the leads on the lens.
A good TC (e.g., OEM Nikon) will be coded to inform the camera of it's existence and factor. In some of the older cameras that was very simple, but entails a chip nowadays. The 3rd party TCs may not have any coding, but depends on what the manufacturer decides to do. If the camera does not know there is a TC attached, the AF may have a higher miss rate.
EBH