Superior Large-Aperture Performance Like other large-aperture Carl Zeiss® lens designs, this f2.0 lens is simply magnificent in its ability to capture brilliant high-resolution images in low-light conditions requiring fully open aperture. SSM (Super Sonic wave Motor) Designed for fast, smooth, silent automatic focusing, this unique technology achieves high torque at low speed with rapid start/stop response. It operates through the ability of a piezoelectric device to reshape itself quickly when voltage is applied. Carl Zeiss® T* Coating Coated optics were pioneered by Carl Zeiss® -- and this superb lens features T* (T-Star) coating that virtually eliminates the lens flare, internal reflection and light scattering that can otherwise occur at glass-to-air surfaces. Glass-Molded Aspherical Lens Elements These precision lens elements correct distortion for sharper, more visually accurate images. ED (Extra-low Dispersion) Glass Because light of different wavelength (or color) bends at different angles when it passes through a lens, ED (Extra-low Dispersion) Glass is used in Carl Zeiss® lenses to eliminate chromatic aberration by correcting certain wavelengths of light for sharp, clear images with well defined colors.