HANDLING: This is a well-made lens, with Sigma’s newer smooth black surface finish that’s more resistant to marking than the older matt black. It’s moderately heavy, and both focus and zoom rings are well weighted and silky smooth — actually the best of the bunch.
FEATURES: Standout feature is the mega-wide zoom, which goes down to an incredible 12mm. This is way wider than anything else -in fact, it’s the widest rectilinear (non-fisheye) lens of any kind made for full-frame. At 122°, the field-of-view is a whopping 15° more than the second widest lens here, the Nikon 16-35mm. The flipside of that is the focal length at the longer end only extends to 24mm, and another downside is the bulbous front element that prevents the use of normal filters. There are specialist grad filter kits available(eg Formatt Hitech), but they’re both enormous and costly, so you’d best bone up on your HDR technique as an alternative -some prefer it anyway.
AUTOFOCUS: With so much depth-of-field available, the ultrasonic AF system doesn’t have much to do, but it does work very quietly efficiently, so you won’t have any problems.
PERFORMANCE: Under the hood, there’s a whole stack of exotic glass and aspherical surfaces, totalling 17 elements in 13 groups. Just as well, as they have a hefty task managing that vast angle-of-view, and delivering sharp images without too much distortion, vignetting and flare. Sigma has done a remarkable job and performance is a lot better than you might expect, in fact it stands shoulder to shoulder with the best, despite its relatively low cost.
The modest maximum aperture, only f/4.5at 12mm rising to f/5.6 at 24mm, gives it bit of a head-start on the optical challenge, but even so the lens is sharp, very sharp, hitting the excellent standard right across a full-frame image from maximum aperture. Only the edges lag a little at the tele end, which is a common characteristic. There’s plenty of distortion.vignetting and chromatic aberration, as there always is with ultra-wides, but the Sigma’s not any worse than most others. Peak resolution is a high 118 lines-per-mm, recorded at 17mm f/5.6 in the centre. An area of caution is to watch out for flare. Given the extensive field-of-view, areas of sky and sun are bound to be included in the frame, and the protruding front element naturally falls victim to picking up specula highlights. This is mostly inevitable, and more something to be aware of than to worry about.
VERDICT: This is an amazing lens. In short, it is sharp, built to a very high quality, has a smooth operation and, all things considered, reasonably priced. And at 12mm, the field-of-view is incredibly wide, producing a unique style of image unmatched by any other lens.zoom or prime. Well worth consideration.