Full image with the bare 600mm lens @ f/5.6 (click on the image for full size)
100% crop with bare 600mm lens @ f/5.6
The bare 600mm is pretty darn sharp - the detail on the fence post is captured pretty well. No surprises here then...
Full image with the TC-17EII Teleconverter mounted on the 600mm lens@ f/8 (click on the image for full size)
100% crop with the TC-17EII Teleconverter mounted on the 600mm lens@ f/8
In the past, I've seen the TC-17 deliver a bigger image without necessarily resolving more detail than the bare lens at the same distance, especially on the 70-200mm f/2.8 VR (version 1). No such complaints here - the quality of the glass on the 600 shines through and really delivers a sharp, usable image. The compromise in aperture hasn't been a big deal for me YET - the D800 seems to take it in stride and focuses swiftly and surely. However, busy backgrounds can still throw it off so you need to give focus a manual tweak every now and then.
Full image with the TC-20EIII Teleconverter mounted on the 600mm lens @ f/10 (click on the image for full size)
100% with the TC-20EIII Teleconverter mounted on the 600mm lens @ f/10
With the TC-20, the image in the viewfinder and on the sensor is certainly bigger, but it looks to be like the detailed resolved is similar to the TC-17. Contrast also seems to take a slight hit. Overall, a decent performance but it loses you more light than the TC-17, slows down AF a little and doesn't really resolve any more detail.
I'm pretty happy with the results the 600mm and TC-17 provide, and can safely say that I'll use this combo whenever I need the reach and don't need the AF speed. I wouldn't say that the AF is speed is bad, but I'm not sure it'll be up to handling birds in flight.
I've always sworn by the performance of the TC-20EIII teleconverter on the 400/2.8, but it looks like the 600 doesn't work as well with this teleconverter. The results are certainly usable, but doesn't provide enough of an advantage over the TC-17 to recommend it. The allure of 1200mm is still too much to resist though, so I'll continue doing more field testing before I discount this combo.
What do you think? Any thoughts and comments are welcome!