On the left is my 2-year-old Nikon TC-14B teleconverter, which is amazingly well-matched to my Nikkor 400mm f/3.5. On the right is my Tamron 140F-FNs 1.4x autofocus teleconverter. The optics are sharp, but autofocus with it is slow.

On the left is my 2-year-old Nikon TC-14B teleconverter, which is amazingly well-matched to my Nikkor 400mm f/3.5. On the right is my Tamron 140F-FNs 1.4x autofocus teleconverter. The optics are sharp, but autofocus with it is slow.

On the left is my 2-year-old Nikon TC-14B teleconverter, which is amazingly well-matched to my Nikkor 400mm f/3.5. On the right is my Tamron 140F-FNs 1.4x autofocus teleconverter. The optics are sharp, but autofocus with it is slow.