The EF 16-35mm f/2.8L II USM is a professional-calibre wide-angle lens with premium optics, a weather seal (perfect for outdoor shots) and a slightly wider viewpoint than the EF 17-40mm. Since perspective, which is the most powerful effect of wide-angle photography, is stronger at shorter focusing distances, close objects appear closer and distant objects (like clouds) appear more distant. Bring more of the surrounding landscape into the frame of your picture with improved edge-to-edge image quality. Notice how you start to see more of the treetops and the sky. As the horizon curls upwards, it kicks off a sense of movement in the scene and brings the brewing stormy sky closer to the forefront. When you start shooting at wider angles, the circular aperture will give you a beautiful and natural background blur. The EF 16-35 has a large 2.8 aperture that allows you to shoot at a lower light level.