Dedicated for Digital SLR Cameras through the employment of an optical design for exclusive use with digital (APS-C) SLR cameras, an ultra wide-angle zoom lens with a focal length equivalent to a 17-28mm when converted to that of a 35mm full size film camera lens has been realized. Using this lens along with the digital SLR-dedicated AF18-200mm zoom lens introduced by Tamron simultaneously, you can enjoy creative digital SLR photography with a wide choice of angles of view. Features an Optical System Optimized for Characteristics of Digital Cameras in order to achieve outstanding optical quality, the optical system uses one element of HID (High Index/High Dispersion glass) to compensate for chromatic and spherical aberrations; one LD (Low Dispersion) glass element to minimize on-axis (longitudinal) and off-axis (lateral) chromatic aberrations that are the greatest hindrance to high optical quality; one high-precision, large clear aperture, glass-molded aspherical element and two hybrid aspherical elements to thoroughly compensate for spherical and chromatic aberrations and distortion. Optical Design Dedicated to Digital SLR Photography by Optimizing the Angles of Incidences of Light Rays Reaching the Image. The zoom lens uses a new optical system designed to confine the changing angles of incidences of light rays reaching the imager within a certain scope over the entire image field from the center to the periphery, by considering the effects of variances due to zooming. Enhanced Peripheral Illumination Peripheral light fall-off is minimized when compared with that of conventional lenses for film cameras so that images are uniformly bright from the center to the periphery. Outstanding Resolution Since the lens is designed exclusively for digital SLR photography, it provides high image quality in terms of resolution, contrast and flatness of image field