OK, some of the Nikon camera's have a threshold of F8, so, in any combination of F stop or converter that goes over F8 you lose auto focus. ie. if you put a 1.4 on a f5.6 lens you get a 200-500 mm zoom F 7.84 lens which means you have to shot wide open to get auto focus. YOU CANNOT STOP DOWN. Most folks are saying that the sweet f stop for this lens has been 6.3. So, the TC-14E 111 at 6.3 would be F 8.82. Which means you can no longer use the auto focus if you stop down to 6.3 on that lens. Bottom line, DON"T DO IT. I use this lens on my D750 and shot birds all day long. With this lens I can shoot almost 95% of what I need. It is my opinion that nothing good comes from TCing this lens.