Sigmas APO 50-500mm F4.5-6.3 DG OS HSM is an advanced optical design of this 10x power high-performance zoom lens that covers the standard-to-super-telephoto range, now with the added advantage of Sigmas own Optical Stabilization which offers the use of shutter speeds approximately 4 stops slower than would otherwise be possible. Sigma is the only one to offer OS for Sony and Pentax mount where the image is stabilized in the viewfinder if chosen. For many photographers, having an "all-in-one" lens is an absolute dream. Especially for nature photographers, the idea of a lens suitable for landscape photography at the short end of the zoom range, while still having enough reach for wildlife is a great option. Add to that, the ability to close focus on small objects in the field such as flowers and its the perfect backpackers lens. Four SLD (Special Low Dispersion) glass elements provide optimum color correction & sharpness throughout the entire zoom range and super Multi-Layer lens coating reduces flare and ghosting and assures high image quality throughout the entire zoom range. With no need to change lenses, there is less chance of dirt or moisture entering the camera and fouling the imaging sensor.