The Sigma 50/1.4 EX DG HSM is a capable f1.4 lens. You can produce shots with good image quality even at a wide open aperture of f1.4 if you don’t look too far into the FX-corner. It’s sharper than the Nikon’s AF-S 50mm f/1.4G and has less longitudinal CAs.
At long distance shots there is an issue in the DX-corner where the lens shows some field-curvature. Bokeh is on a pretty satisfying level – in the background as well as the foreground. That justifies a price that is a bit higher than for an equivalent lens from Nikon.
All-in-all it is a good f1.4 lens which you can well use at the largest aperture although you have to accept at f1.4 the corners are soft. But that may not be a bad thing depending on your type of photography. And although the lens does not do contrast-based AF in live-view or movie-mode on my D800 I’d say that manual focus in both modes often is a viable alternative. The functionality of contrast-based AF may also be better on other camera-bodies. And normal phase-detect AF through my DSLR viewfinder was fast and reliable. So I’d still award the Sigma 50/1.4 a Recommended rating. Below I have summarized the good and bad points of the Sigma 50mm f/1.4 EX DG HSM for you.