This is a SIGMA-made lens that sports a Nikon F mount. The aperture of the lens is maximum ƒ/5-6.3 and minimum ƒ/22.
From London Camera Exchange
Sigma 100-400mm F5-6.3 DG OS HSM Contemporary - For Nikon
Ecprof
729955 - 100-400mm f/5-6.3 DG OS HSM I Contemporary Lens for Nikon F M
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