Sigma 500mm
Nikon 300mm F4 w / vs Sigma 50-500mm Tele?

I am thinking of buying a lens in the near future to use to surf photography. Am looking for old Nikon 300mm F4 and the Sigma 50-500mm. Both are about the same price used. I would be using the Nikon with a 1.4x TC as a 420mm F5.6. In terms of image quality, which would be better in the same area 420mm, the Sigma or Nikon TC?

The Nikkor 300 mm f / 4 with the show without limitations. You really have to try to see which performs best with 300 mm Nikkor Nikon Teleconverter is an excellent combination, however, I have a friend who shoots sport and you just pick up the Sigma 500-500 mm and has had no problems with it so far in terms of image quality is concerned. The real test is how it performs within ten or fifteen years.