Just wondering about any comparisons between a Nikon 14mm f/2.8 AF-D prime compared with Rokinon, Sigma, and Tamron prime counterparts. I've read reviews but am not seeing the Nikon coming out way ahead of the Sigma or Rokinon. I'm not interested in a zoom because of price. Between these 3-4 manufacturers, can you tell me any pros/cons? Thanks!