The Sigma 18-35mm f/1.8 DC HSM A1 is a high-quality zoom lens designed specifically for Pentax K-mount DSLRs. Key features include:

Fast f/1.8 Aperture Zoom: While most zoom lens apertures top off at f/2.8, the Sigma 18-35mm bests that by 1 1/3-stops. This enables stellar low-light shooting, as well as providing full-frame like depth-of-field on a crop-frame camera.

Wide to Normal Range: With a 35mm-equivalent focal length of 27mm-53mm, it covers your wide to normal range. This makes it a great option for landscape, event, and street photographers.

Hyper Sonic Motor Autofocus System. Provides fast, smooth, and quiet operation in a wide variety of shooting situations. You can also manually override the autofocus motor at any time by rotating the focusing ring, giving you quick fine-tuning ability.

High Build and Image Quality: As a member of Sigma’s Art lens line, it goes through Sigma’s rigorous A1 testing, ensuring high image quality. Optically, four aspherical and five SLD glass elements are used to minimize distortion and aberrations throughout the zoom range, with Super Multi-Layer coatings for eliminating lens flare and ghosting. The barrel is made of a lightweight TSC compound that gives the lens a solid, sturdy feel. Internal focusing and zooming further back this claim.