The 120-400mm f/4.5-5.6 DG APO OS HSM Autofocus Zoom Lens from Sigma is a telephoto zoom lens for use with Pentax DSLR cameras. The lens features built-in Optical Stabilization (OS) for sharper photos, and a Hyper-Sonic Focus Motor (HSM) for quick and quiet autofocus.

Its optical formula is highlighted by three Special Low Dispersion (SLD) glass elements, which serve to correct color and preserve sharpness throughout the entire 3.3x zoom range of the lens. Its rear focusing system corrects for aberration fluctuations caused by focusing.

The lens, which is only eight inches in length and weights a mere 3.9 pounds, ships with a lens hood, a removable tripod collar, front and rear caps, and a carrying case. It can be used with Sigma APO teleconverters for those times when you require a longer focal length. While it is not a true macro lens, its innate close focusing capability makes it a great use for capturing smaller objects including flowers -- without having to change to a dedicated macro lens.

Because most Pentax cameras feature in-body image stabilization, the lens provides you with the option of disabling the in-lens stabilization during use -- giving you the flexibility to use the image stabilization of your choice: in-body or in-lens. Owners of legacy bodies that do not have stabilization will find this option especially useful. Of course, you can disable the stabilization feature in both the lens and the body for those times when it is appropriate to do so, such as when you are using a tripod.