Jim Bob wrote:
Interesting. I don't have a teleconverter. But I did some extensive testing with the lens in a light controlled setting. I found that it is just a tad sharper than the Sigma and Nikon at f/8 if pixel peeping. But for all intents and purposes the lenses were too close to call. I do prefer the Sigma and Nikon quicker focus. I haven't attempted manual on the Tamron yet.
I have not done much testing, as you know, but in general I would not waste my money on the converter. Imagemeister posted a shot with the D500/G2 at a pretty good distance recently.