The f/2 maximum aperture and 13-element optical design with aspherical and ED glass deliver strong low-light performance and sharpness in a compact 370g body. Its all-metal, weather-sealed I Series construction and tactile aperture ring provide a premium handling experience rare at this size. This lens is best for environmental portrait and astrophotography shooters who need a fast, ultra-wide prime that won't weigh down a kit.