The Pentax SMCP-DA* 16-50mm f/2.8 ED AL (IF) SDM Lens is a high-quality bright f/2.8 lens designed exclusively for use with digital SLR cameras. This lens brings together advanced optical technologies, including aspherical elements, special optical-glass elements, and original lens coatings. It offers a versatile ultra-wide to medium-telephoto zoom range, and can be used as the ideal standard zoom lens in a wide variety of applications, including landscape, snapshot and portrait. Pentax DA* (DA-Star) zoom lenses come equipped with the SDM System, which assures smoother, quieter auto-focusing operation by using a built-in supersonic motor. When mounted on the K10D digital SLR camera body, the focus mode is automatically switched to SDM-assisted auto-focusing. When mounted on older Pentax digital SLR camera bodies, the conventional autofocus mode using a camera-mounted motor is selected. Note: Not suitable for 35mm film SLR cameras.