SIGMA 28mm f1.8 EX DG Aspherical Macro is one of several EX-Series lenses. This lens has a fast F1.8 maximum aperture, with macro-focusing capability. It features minimum focusing, down to 20cm/7.9 inches (reproduction ratio 1: 2.9). The iris diaphragm has 9 diaphragm blades to obtain beautiful out of focus image. It incorporates the floating focus system and the use of two aspherical lens elements to minimize distortion, spherical aberration and astigmatism. The lens incorporates minimum vignetting optical construction in order to obtain adequate peripheral brightness with open aperture. Internal focus system of the lens eliminates front lens rotation, thus allowing the use of a Perfect Hood and easy use of polarizing filters. The lens also incorporates a dual-focus mechanism. It is easy to hold the lens, since focusing ring does not rotate during auto-focus, and yet provides adequate torque of the focusing ring during manual focusing of the lens. The lens materials used in this lens are lead and arsenic free ecological glass.