SIGMA 12-24MM F4 DG HSM | A
What it lacks in speedy aperture rating, it more than makes up for in maximum viewing angle, stealing a lead on the other contenders
a couple of millimetres might not sound like a big deal but, in this class of lens, a single millimetre equates to roughly an extra 3.5 degrees in viewing angle, at the short end of the zoom range. as such, this lens gives a noticeably wider maximum viewing angle than any of the others on test; it works out to 122 degrees compared with the Tokina’s 107, measured on the diagonal of the frame.
whereas the previous ‘Mk ii’ edition of the lens had a variable f4.5-5.6 aperture rating, the new art version represents a complete redesign with a constant f4 aperture. it’s bigger and heavier, but very well built, gaining fluorine coatings on the front and rear elements and a weather-seal ring around the mounting plate.
The new optical layout includes a highly technical, extra-large-diameter aspherical element at the front, along with two further aspherical elements and five premium FLD (Fluorite-grade Low Dispersion) elements. a revamped ringtype ultrasonic autofocus system boasts an increase in torque, which results in faster yet equally quiet autofocusing. an electromagnetically controlled aperture is featured in the nikon as well as canon mount version of the lens. Like most ‘Global vision’ lenses, this one is compatible with sigma’s optional UsB Dock for fine-tuning performance and applying firmware updates.
centre sharpness is excellent even at f4, while corner sharpness also becomes very impressive when stopping down by just a single stop. The sigma compares very favourably with canon’s super-pricey 11-24mm lens in this respect, and beats it for control over colour fringing and distortion. indeed, distortion is remarkably low for such a wide lens. another bonus for canon shooters is that the full range of in-camera lens corrections is available, as per own-brand canon lenses. For nikon, only vignetting correction is officially supported.