Pentax SMC DA Series 50-135mm f/2.8 ED IF SDM Telephoto Zoom Lens for Pentax and Digital SLR Cameras 50-135mm telephoto zoom lens with F/2.8 maximum aperture for Pentax digital SLR cameras Aspherical elements, special optical-glass elements, and original glass coatings Tightly sealed weather- and dust-resistant housing stands up to rainy or dusty conditions SDM system produces smooth, quiet autofocusing; SP coating protects exposed lens elements Measures 3 inches in diameter and 5.4 inches long; weighs 24.2 ounces without hood