Please refer to Making Sharp Images for discussion and examples of how to read MTF charts, as well as the very real issues of build quality and testing for a bad lens or camera.
The presence of mild astigmatism suggests a trace of lateral chromatic aberration might be present, and this indeed is the case in field shooting. Field curvature might also be present, and the modest performance outside the central 2/3 area (15mm offset) suggest that this lens would best be used on a DX format sensor.
Nikon doesn’t publish MTF other than wide-open, but field shots show a marked improvement at f/5.6, so f/4 should be avoided on full-frame cameras; stop down to f/5.6 if feasible.
Remember that a real physical lens can only approach its as-designed specifications, and might not meet this ostensible performance level due to build variation/errors.
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Since 2006, Diglloyd Advanced Photography is the authoritative review and reference for DSLRs and their lenses: Canon and Nikon primarily, but also Pentax and some medium format. Reviews of key DSLRs are included, but the primary focus is on lens performance. Also included is a wealth of technique and workflow approaches.
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