Sigma 28mm F1.4 DG HSM A is an Auto Focus (AF) Wideangle Prime lens with 35mm FF max sensor coverage. When mounted on a 35mm FF sensor camera, it will give you an FF equivalent focal range of 28mm. Providing a max aperture of f1.4 at 28mm, this lens is very fast.
Sigma 28mm F1.4 DG HSM A is weather sealed which makes it an ideal lens for outdoor use, especially when coupled with a weather sealed camera body.