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.
Performance wide open at f/1.4 is outstanding. Large structures are rendered with very high contrast at f/1.4, and fine details are rendered with a contrast not achieved by some lenses even at f/8.
There appears to be little field curvature, and only a modest loss of sharpness at the corners of the frame, a remarkably consistent corner-to-corner performance. Field shooting suggests a mild rearward curvature starting at the edges and increasing to the corners (objects at a further distance in the corners than the center will be slightly sharper than expected).
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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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