I have a Canon 5D and have recently purchased an NN5 w RD16 & Ezyleveller II. I am contemplating purchasing a new lens. I currently use a 24-105mm f4 but am looking at either an EF15mm f2.8 or an EF28mm f2.8. At the moment I'm learning how to use the NN5 and am taking simple single plane panos. Which lens should I purchase and why?