Sigma 15mm f/2.8 EX DG Diagonal Fish-Eye for NikonThe Sigma 15mm f 2. 8 EX DG Diagonal Fisheye holds a unique position in the Sigma lens line up. The 15mm is a diagonal fisheye which means the distorted scene is shown full frame within the cameras field of view. Using acute perspectives not seen by the human eye, this lens is an essential for taking eye capturing images. The large f 2. 8 aperture makes the 15mm capable of overcoming any lighting situation. DG for Digital Sigma's DG lenses are