TAMRON SP 17-50MM F2.8 XR DI II LD NIKON
Extra Refractive Index
More compact lenses with superior image quality XR (Extra Refractive Index) glass can bend light rays at steeper angles thereby decreasing the physical length of the lens while enhancing imaging performance by minimising optical aberrations. With its superior light-bending power XR glass makes it possible to design a short-barrel lens with the same light-gathering ability (aperture value) as a long-barrel lens Ð even with a smaller lens diameter. By using this principle Tamron has been able to shorten the length of the entire optical system and produce lighter more compact lenses of the same speed and also to provide greater zoom ranges in lenses that are much more convenient to carry and hand-hold. XR glass is costlier than conventional glass but it yields enhanced optical power distribution making the innovative XR lens designs possible.
Flower-shaped hood is supplied with the lens to shield stray light
Included as a standard accessory the flower-shaped hood matches the rectangular shape of the image sensor to most effectively block the interference of superfluous light rays entering from outside the borders of the image area helping to ensure sharp clear flare-free images with crisp detail in the shadow areas.  Fast standard zoom lenses with an f/2.8 maximum aperture throughout the entire zoom range used exclusively for digital SLR cameras with APS-C sized image sensors. As of 15th December 2005. Based upon Tamron research of lenses in the same class. As APS-C sized image sensors are smaller than 35mm film the 17-50mm can fill the frame with almost the same scope as a lens with a maximum magnification ratio of 1:3.0 on a 35mm SLR camera.
Lightweight compact fast standard zoom designed exclusively for digital SLRs with 17mm wide-angle coverage
Exclusive design for digital SLR cameras achieves a fast standard zoom lens that covers virtually the same angles as focal lengths of 26-78mm when converted to a 35mm format. The wide-angle focal length is established at 17mm (26mm equivalent) to obtain a wider angle of view than ordinary standard zoom lenses. Complicated mechanisms are built into this compact profile for excellent portability and ease of use. A complex triple-cam structure, where cams zoom and focus within a three-layer lens barrel, improves AF focus precision for close-up shots and control of torque when zooming. A comprehensive engineering overhaul has downsized its parts and increased their precision and durability, making the body lightweight and compact with a filter diameter of 67mm, overall length of 81.7mm (3.2”)*, and weight of 434g (15.3oz.)*. * Values given are for Nikon AF cameras.
Revolutionary minimum focus distance of 27cm over the entire zoom range provides a 1:4.5 macro capability
The lens achieves a minimum focus distance of 27 cm (10.6”) over the entire zoom range, the best in its class. The maximum magnification ratio of 1:4.5  at the 50mm setting is the top level in its class.
Super Performance series
Performance takes priority for superb image quality This line of ultra-high-performance lenses is designed and manufactured to the exacting specifications demanded by professionals and others who require the highest possible image quality. The foremost priority is achieving superior performance parameters – high design standards take priority over cost constraints. As a result, Tamron SP lenses feature innovative designs that have established an enviable reputation for excellence amongst demanding photographers.