In order to assure the exceptional imaging power demanded in the new-generation, high-performance Star series, this new lens incorporates high-grade Super ED (Extra-low Dispersion) glass optical elements and an aspherical optical element to compensate various aberrations to a minimum — in particular, to effectively minimize axial chromatic aberration to prevent the generation of purple fringing in backlit situations. It also reduces distortion — a serious concern in portrait photography — to nearly zero at a focusing distance of four meters.

...

In addition, PENTAX has developed a new ring-type SDM exclusively for this new lens to realize flawless, high-speed autofocus operation, while adopting an exterior design providing a firm grip to facilitate manual-focus operation. This new lens is designed not only to assure the highest imaging power currently possible, but also to optimize the joy of picture-taking. 
*Please apply the latest updater of Digital Camera Utility 5 when you handle images taken by this lens on Digital Camera Utility 5. In case the software version is old, the name of this lens can not be displayed correctly. Digital Utility 4 and below can not display the name of this lens correctly.
*Contrast detection AF during live view may not be in focused with the K-S1.