Both Tamron and Sigma have established themselves as creators of high-quality but affordable lenses that significantly undercut the prices of first-party manufacturers. For anyone looking for a super-telephoto zoom lens, the Sigma 100-400mm f/5-6.3 DG DN OS Contemporary and Tamron 150-500mm f/5-6.7 Di III VXD are both affordable and offer impressive performance. This great video review compares the two to help you pick the right one for your work.