This 17-50mm is an extremely high-quality standard zoom with a high luminosity of 2.8 over the entire focal length range. It belongs to the Super performance ( SP) class of Tamron lenses distinguished by ultra high optical and mechanical quality. The high luminosity that this lens offers is ideal for low-light conditions and professional image composition. The result is images with smooth, even bokeh (background blur), where the subject is virtually released from the background. Apart from the unlimited possibilities that this lens has to offer, it is the quality of your images that stand in the focus. The world´s shortest minimum focus distance of only 27 cm was achieved, by using 3 XR glass elements (Extra Refractive) in the front group coupled with a new mechanical design, whilst at the same time keeping the construction compact. The maximum magnification ratio of 1:4,5 and a weight of mere 430 g are also a worldwide top*. Image defects are kept at an absolute minimum through the application of aspherical elements and LD (Low dispersion) glass as well as a special coating of internal glass surfaces (Internal Surface Coating). The result is high-quality extremely sharp and excellent images. *based on lenses of the same class and F/2,8 Please note that Di II lenses are made for the exclusive use on digital SLR cameras with image sensors smaller than 24mm x 16mm. Di II lenses cannot be used together with a full format or 35mm SLR camera, as their image sensors are not able to cover the entire area of full format resulting in dark corners of the (i.e. vignetting becomes noticeable). Please note: The 17-50mm became available with a built-in motor for the Nikon D40, D40X and D60 (Model A16NII) from March 2008. The A16N model which had been available up until March 2008 is only compatible with the D40/D40X/D60 in the MF mode due to the fact it doesn´t have a built-in motor.