What I can tell you is this: the Tamron won me over immediately. Images were razor sharp through the aperture range and with f/22 an option at the slow end, this lens is just at home facing a sunset-spiked mountain range with a fill flash as it is capturing candids at dusk with no flash whatsoever. I could read about now the Nikkor's auto focus is markedly faster, but if I simply asked myself if I had ever missed a shot because the Tamron was too slow, the answer is a definite "no".

It became clear that both Tamron and Sigma had figured out that they would never crack the branding coup that L-series and Nikkor lenses have enjoyed for decades. Their only solution to shake things up and capture any significant market share was to put everything into rivaling Canon and Nikon's optics and build quality and the price similar focal lengths well enough below their lofty competitors that getting 90 or 95% of the lens for $800 less is a no brainer for anyone not having their gear purchases subsidized by an employer.