DxOMark tested the Sigma 24mm f/1.4 DG HSM lens for Canon mount ($849). Here is their conclusion:
Although at first sight the Sigma’s overall DxOMark score might not look as convincing as the two previous Art models from the maker, it is important to look deeper than the numbers suggest, especially at shorter focal lengths. The Sigma 24mm f1.4 DG HSM is the finest 24mm we’ve seen, although against the Canon 24mm f1.4L II USM, it’s a close-run thing. That model has slightly higher peak sharpness centrally at f4-5.6, but the Sigma has more uniform performance overall, including superior control of CA and distortion. It’s a worthy addition to the range and will only add to the maker’s reputation. Plus at around half the price of the Canon L-series equivalent, it’s a steal.
