What assumptions do you think are being made? Did you look at the images, and do you think the 600 6.3 one is in focus?
I've looked at it on 3 different setups (iPhone, 45" 5K2K monitor, 77" TV) and it's clear as day that it isn't in focus.
Yes of course I looked at the images. Duh. And yes, on a big monitor. The assumption you and others are making is that because it is slightly soft, it is not in focus. What if that is as good as it gets with that lens and TC combined? Things behind and in front of the "eye" of the target are softer than the region around the eye. That says to me that this was focused on the eye and not in front or behind.
TC's do degrade image quality. I have seen it with my 1.4x and big time with the 2x. So much so that I got rid of the 2x. I could see sharpness and micro contrast reductions with the 1.4x and significant reductions with the 2x across multiple lenses including the 300 f2.8.
FYI, I have no skin in the game. These are fantastic lenses and will service people well. The degree to which people attach anyone putting up images that don't meet their personal expectations is a bit over the top these days on this forum. None of us commenting on the post took these photos. It is only one data point and someone's conclusion based on their methodology that they have found works for them. Would I do it differently, sure. I have my own methods and ways to make assessments. I am sure others here would rip them to shreds as well. That is why I don't post them.
