Designed to rival the primes, this zoom's optics have been revamped to provide even greater resolution, clarity, and bokeh quality. Bright f/2.8 constant aperture allows users to capture images in dim lighting conditions and with a shallow depth of field. One Super ED (extra-low dispersion) and Two ED elements effectively suppress chromatic aberrations and color fringing for greater clarity and color fidelity. Five aspherical elements, including three extreme aspherical elements (XA), minimize spherical aberrations, distortion, and also reduce 'onion ring' bokeh. Faster focusing performance, improved close-up shooting, and enhanced control are all benefits of the redesigned focusing system. Four XD (extreme dynamic) linear motors contribute to greatly improved focusing performance, compared to the DDSSM system of the predecessor, including faster, quieter, and more precise AF that's ideal for both video and stills. Faster AF means improved focusing when working with fast-moving subject