Thanks everybody! This was from a camera experiment. The setup was a Nikon Z6, Fringer Canon EF adapter, Kenko Teleplus HD 1.4 TC, Canon 400mm 5.6L lens. I was surprised it even worked at all lol! But it will NOT become my regular setup - the hit rate was abysmal and AF unreliable and slow for action shots. But it was a fun "what if" experiment!