Covering a range of useful telephoto focal lengths, the HD PENTAX-D FA 70-210mm f/4 ED SDM WR from Pentax is a flexible zoom characterized by its reach, range, and relatively sleek design. It features a constant f/4 maximum aperture that maintains consistent brightness throughout the zoom range and offers increased control over depth of field for achieving selective focus effects. The optical design incorporates a series of low dispersion elements that help to minimize chromatic aberrations in order to achieve greater clarity and color accuracy and a multi-layer HD Coating also helps to suppress flare and surface reflections for improved contrast. Complementing the optics is an SDM autofocus system that delivers especially quick, quiet, and accurate focusing performance that suits both stills and video applications. Additionally, the lens is moisture-resistant and has a Super Protect coating on the front element to enable its use in trying environmental conditions.