To achieve an F2.8 aperture at all focal lengths, it employs three aspherical Lenses to provide optimum aberration compensation. Two Special Low Dispersion (SLD) glass elements are provided for color aberration compensation, to assure high image quality.It incorporates "Super Multi Layer Coating" to reduce the influence of harmful light caused by reflections from the digital image sensor.Two SLD elements, one Glass Mold Aspherical plus two Hybrid Aspherical lenses provide excellent correction of various aberrations and a high level of optical performance.The lens has a minimum focusing distance of 40cm (15.7 inches) at all focal lengths and is capable of macro photography with a maximum magnification ratio of 1:3.8.This lens incorporates a Dual Focus (DF) system that is designed to make the lens easy to hold during autofocusing, and yet provides a large focus ring for easy manual focusing.