The tamron sp af 17 50mm f28 xr di ll ld aspherical if pentax fit lens is a lightweight compact fast standard zoom lens designed exclusively for use with digital slr cameras aps c size the wide angle focal length of 17mm equivalent to 26mm obtains a wider angle of view than the standard zoom lens without any increase in size or weight the fast f28 aperture gives a natural out of focus effect which is great for portraits whilst the minimum focusing distance of 27cm over the entire