This shows the softness of the older 20E doubler converter with the
300mm f2.8 AF-S lens. I closed down 1 stop, still a very soft photo.
Th newer TC20Eii or III are better, TC14 or 17 are fine with the 300 lens.
Nikon D810 1/6400s f/5.6 at 600.0mm iso640
300mm f2.8 AF-S w/ TC20E
full exif