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.

Telephoto zoom is designed for full-frame Pentax K-mount DSLRs, however can also be used with APS-C models where it provides a 105-315mm equivalent focal length range.

Constant f/4 maximum aperture affords consistent brightness throughout the zoom range and offers improved control over depth of field.

Three extra-low dispersion elements and two anomalous dispersion elements help to reduce chromatic aberrations throughout the zoom range in order to improve clarity and color accuracy.

Multi-layer HD Coating has been applied to individual elements to reduce surface reflections, flare, and ghosting for greater contrast and color fidelity when working in strong lighting conditions.

Ring-type Supersonic Direct-drive Motor (SDM) delivers quick, quiet, and precise focusing performance to suit working with moving subjects. A Quick-Shift Focus System also allows for quick switching between AF and MF settings and a two-type focus range limiter helps to quicken focusing times.

Internal focusing and zooming mechanisms maintain the overall lens length during use for easier, more intuitive handling and faster performance.

A moisture-resistant construction benefits this lens' use in inclement conditions, and an SP (Super Protect) coating has also been applied to the front lens element to guard against dust, dirt, and smearing.

Rounded nine-blade diaphragm contributes to a pleasing bokeh quality.

Electromagnetic diaphragm enables more accurate exposure control during video recording. This mechanism is available only when used in conjunction with K-1 Mark II, K-1, K-3 Mark II, K-3, KP, K-70, K-50, K-S2, and K-S1 cameras.