Sigma 16-28mm F2.8 DG DN Lens for L Mount with External Hard Drive, and Memory CardSigma 16 28mm F2. 8 DG DN Lens for L Mount With its excellent field curvature correction, the 16 28mm F2. 8 DG DN is able to achieve exceptional edge to edge sharpness, which is essential for most wide angle applications. It boasts five FLD elements and four aspherical lens elements to ensure optimal image quality with minimal aberrations. The lens has an inner zoom mechanism that keeps overall length consistent throughout the entire zoom range,