Digitally Integrated Design, is a designation Tamron puts on lenses featuring optical systems designed to meet the performance characteristics of digital SLR cameras.
Revolutionary downsizing "XR" technology employed by Tamron in the development of high-power zoom lenses such as the 28-200mm and 28-300mm, is translated into the design of the 28-75mm f/2.8 making this lens possibly the smallest and lightest in its class. Its compactness makes it look and feel like an ordinary standard zoom lens, yet has the versatility that a fast constant maximum aperture offers.
Visit Tamron's interactive site for more information on focal length
and depth of field