Used mainly for filming weddings and some family photos. The aperture fixed turns it great for low light sessions. As said in the brand website: Large aperture standard zoom lens with a minimum focal length of 17mm, designed exclusively for digital SLR cameras and incorporating Sigma’s original OS (Optical Stabilizer). The OS function offers superior Stabilization. The lens has a compact construction with an overall length of 91.8mm. This compact and lightweight construction makes the lens ideal for travel photography. Two FLD (“F” Low Dispersion) glass elements, two glass mold and one hybrid aspherical lens provide excellent correction for all types of aberrations. This lens has superior peripheral brightness and provides sharp and high contrast images even at the maximum apertures. The incorporation of HSM (Hyper Sonic Motor)