Overview

The Sigma 400mm f/5.6 APO is a vintage telephoto prime offering good sharpness wide open, especially at f/5.6, with APO correction reducing chromatic aberration. Its compact, lightweight build (960g–1435g depending on version) and internal focusing make it travel-friendly. Weaknesses include a stiff built-in hood and loose AF/MF switches on some samples. Best suited for wildlife and sports photographers seeking affordable reach, it performs optimally around f/8–f/11.