Premium G Lens optical design This 16-55mm (24-82.5 mm full-frame equiv.) standard zoom lens weighs in at only 494g. The advanced G lens design includes two Advanced Aspherical and two Aspherical elements to suppress abortion and three ED (Extra-low dispersion) glass elements and Nano AR coating to suppress reflections, flare and ghosting. The 9-blade circular aperture contributes to gorgeous bokeh while the XD (Extreme Dynamic) Linear Motor offers fast, precise, quiet AF and tracking F2.8 max aperture The F2.8 max aperture maintains exposure and depth of field, allowing you to isolate your subject from the foreground and background with amazing light gathering capabilities when shooting wide open. When changing your aperture to defocus the background, the areas out of the focal plane appear blurred. This 'bokeh' effect of the blurred background is enhanced with circular aperture blades used in this lens. 9-blade circular aperture contributes to gorgeous bokeh The 9-blade circular aperture maximizes the beauty of this large-aperture prime-lens, contributing to impressive images in which the subject stands out against a smoothly defocused foreground and background, as well as perfectly round points of defocused light. Conventional aperture blades have flat sides that create unappealing, polygonal-shaped defocused points of light. Alpha lenses overcome this problem through a unique design that keeps the aperture almost perfectly circular from it