The lens + teleconverter combo is sharp, but autofocus slows down
I went out again with the Nikon 180-600mm f/5.6-6.3 Z Nikkor, and this time I used the Z teleconverter TC 1.4x. This combination delivers the equivalent of a 250-840mm f/7.8-9 lens. Again, I’m still using a Nikon Z6 body, so autofocus performance is slower than what you’d see with a Nikon Z8/Z9.
Autofocus definitely slowed down a bit when using the teleconverter, but once focus was acquired it did a good job of staying locked in. What I found from my test shots was that sharpness across the frame was still excellent, even wide-open. Stopping down to f/11 improved edge sharpness slightly, but not enough to make me feel like I needed to do so. I feel that if you can handle the light-loss penalty (1-stop), and reduced AF performance, go ahead and use this combination wide-open. It’s very very good.
Here are a few full-resolution sample images from the Nikon 180-600mm f/5.6-6.3 Z Nikkor + Nikon Z teleconverter 1.4x. Click on any image to view it full-size.