With a price-tag that is only just shy of £300, Sigma's 30mm optic is on the pricey side for a 'standard' lens and with good reason since it comes with an exceptionally fast f1.4 maximum aperture...
As its DC designation indicates, the lens is suitable for use only with sensors up to APS-C size, which includes the non full-frame Canon and Nikon bodies as well as Pentax, Sigma and Sony cameras. Thanks to its considerable size, the lens feels very robust and handles beautifully. Sadly, its manual focusing lacks the silky smoothness that the lens’s overall appearance might lead you to expect. Being that much bigger overall than its peers, the Sigma’s filter ring is a considerable 62mm although there is also an external bayonet fixing for a lens hood.
The lens produces very consistent results across the most useful part of its aperture range, from f/4 to f/8. Wide-open performance is weaker but not unacceptable and the resolution figures are almost always between 0.2 and 0.3 cycles/pixel. That said, something very strange happens at f2.8, where the edge-performances converge before crossing-over but this behaviour does not mar the images visibly in any way.
Bearing in mind that this lens is both faster and more expensive than similar lenses, and that it is a third-party alternative to camera manufacturers’ own optics, the chances are that Sigma’s lens will be chosen and enjoyed by people who really need the extra benefits that its f/1.4 maximum aperture offers