he Pentax SMCP-DA 17-70mm f/4 AL (IF) SDM Lens is a high-quality fixed-aperture f/4 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 wide to medium-telephoto zoom range, and allows for a wider range of shooting applications over the more standard zoom lenses.
This lens comes equipped with the SDM focusing system, which assures smoother and quieter auto-focusing operation by using a built-in supersonic motor. Since this lens only has electrical contacts to communicate between the lens and the camera, autofocusing will only be possible with DSLR cameras that support SDM (e.g. KP , K-70 , K-3 , K50 , K-3-II , K10D, K20D, K100D Super, K200D, and later models). When mounted on older Pentax digital SLR camera bodies, only manual focusing will be possible.