ED glass and Nikon's SIC (Super Integrated Coating) ensures high-contrast pictures, with better color balance even at large apertures. This is one of Nikon's very first lenses to benefit from the ultra-low reflectance SIC coating technology, and benefit it does, with a total of 28 glass to air interfaces. With so many glass/air interfaces, more conventional coating technology would result in very low contrast, unsharp appearing shabby photographic results.
This is one amazing lens. It is one of the very sharpest and highest contrast lenses in its range. This judgment is not limited to zoom lenses but extends to single focal length or prime lenses anywhere within its range. It maintains constant brightness throughout as it is focused. With other macro/micro lenses the lack of constancy of exposure for close focus is a real issue. It turns what would otherwise be difficult to do tasks employing several lenses at various distances from the subject matter into easy tasks using a single lens at a single camera to subject distance. It is an unqualified and uncompromised joy to use.