Sigma 100-300mm f/4 EX DG IF HSM APO Fast Aperture Telephoto Zoom Lens for Pentax and Samsung SLR Cameras Large f4 aperture with minimal light fall-off for bright images Inner focusing system allows attachment of petal-shaped hoods and filters Special low dispersion glass for high image quality Focal length: 100 to 300 millimeters Designed for Pentax digital SLR cameras