The Pentax 18-55mm f/3.5-5.6 is the ''kit'' lens sold with the K10D and K100 (and previous ''*ist'') digital SLR cameras. It is designed to fit a camera with an APS-C (''subframe'') sensor, so while it will mount on Pentax film bodies, it will show obvious vignetting to some degree.
Small and light, the 18-55mm represents a field of view of approximately 28-80mm in 35mm terms. To economize and create a more efficient design, the lens is equipped with a variable aperture; as the zoom extends the focal length, both the smallest and the largest aperture changes. Read the whole review here & you can buy the lens here